1070 Unit 2 Ch9.pdf PDF

216 Chapter 9 amino aCids and proteins A CASE IN POINT (continued) 3. What urinalysis result(s) led to your probable...

216 Chapter 9 amino aCids and proteins A CASE IN POINT (continued) 3. What urinalysis result(s) led to your probable 7. Describe what you would expect to see in this diagnosis? patients protein electrophoresis. 4. Are the abnormal chemistry tests consistent with 8. Which specific proteins would be decreased? the probable diagnosis? Explain why or why not. Which specific proteins would be increased 5. Discuss the physiological cause of the edema. 6. What is Judys A/G ratio? Is it within the reference range? Is it consistent with the probable diagnosis? Whats Ahead 1. A discussion of protein structure, synthesis, metabolism, and 4. A review of the most common total protein and albumin functions. methodologies. 2. An overview of the more common aminoacidopathies. 5. A summary of the major causes of hyperproteinemia, hypopro-teinemia, 3. A description of the specific proteins that are most clinically hyperalbuminemia, and hypoalbuminemia. significant. 6. An overview of protein electrophoresis, including the most com-mon abnormal patterns. INTRODUCTION valine, leucine, isoleucine, phenylalanine, tryptophan, methionine, threonine, and lysine; and in infants, two additional amino acids: Proteins are complex polymers of a@amino acids that are produced arginine and histidine. byliving cellsin all forms of life. Eachprotein is composed of a max-imum The structure of amino acids is amphotericcontaining of 20 different amino acids in varying numbers and sequences. two ionizable sites, a proton accepting group (NH2), and a proton All proteins contain carbon, hydrogen, oxygen, and nitrogen, and donating group (COOH). At physiological pH, approximately 7.4, some contain sulfur. The average content of nitrogen is 16%, and its the COOH easily loses a hydrogen ion and becomes COO-, and presence differentiates proteins from carbohydrates and lipids. NH2 gains the hydrogen ion and becomes NH3 +. Whenboth are Proteins are involved in many cellular processes, including ionized, the amino acid is called an ampholyte, dipolar ion, or maintenance of colloidal osmotic pressure, coagulation, and trans-port zwitterion (the older nomenclature). of various molecules, which will be discussed under protein The isoelectric point (pI) is the pH at which the amino acid functions. This chapter will concentrate on the proteins, protein or protein has no net charge and the positive charges equal the methodologies, and aminoacidopathies that are most clinically sig-nificant negative charges. The pI can vary from pH 3 to 10, and there is no or that you are more likely to encounter in the clinical pH at which all 20 amino acids are neutral. At a pH greater than laboratory setting. the pI, the protein carries a negative charge; at a pH less than the pI, the protein carries a positive charge. For example, if the pI of PROTEIN STRUCTURE a protein is 7.8 and the pH is 8.6, the protein will be negatively Amino acids contain an amino group (NH2), carboxyl group charged. (COOH), hydrogen, and an R group (radical or side chain) with Amino acids in proteins are linked to each other through pep-tide the formula RCH(NH2)COOH. The nucleus of the amino acid bonds. A molecule of wateris split between the carboxyl group is the a@carbon to which the carboxylic and amino group are of one amino acid and the amino group of another, and a cova-lent attached. The radical group is what distinguishes one amino acid bond called a peptide bond is formed, as seen in Figure 9-2. from another. The simplest amino acid is glycine, illustrated in The end of the protein that has the amino free group is called the Figure 9-1 , which has a hydrogen atom asits R group. N-terminal end, and the opposite end that has the carboxyl free Although all amino acids can be synthesized by some animals, group is called the C-terminal end. in higher life forms, including humans, some amino acids called essential amino acids are not synthesized and must be ingested O in the diet. In human adults, there are eight essential amino acids: COO-OH + NH3 + C N + H2O O H Carboxyl group Amino group Peptide bond H2NCH2 C 1st amino acid 2nd amino acid FIGURE 9-1 Glycine. FIGURE 9-2 Peptide bond.  Chapter 9 amino aCids and proteins 217 A peptide contains two or more amino acids. Dipeptides, tri-peptides, of a simple protein and carbohydrates, which make up less than 4% tetrapeptides, and ogliopeptides contain two, three, four, of the total weight. Mucoproteins are linked with large, complex and up to five amino acids, respectively. Polypeptides contain more carbohydrates(74% of the total weight). Nucleoproteins are a than five amino acids. When the number of amino acids exceeds combination of a simple protein and nucleic acids (DNA, RNA). 40, the molecule takes on the properties of a protein chain. In Conjugated proteins without their nonprotein groups or ligands serum, proteins average 100 to 150 amino acids. are called apoproteins; for example, when lipids are freed from a Protein structures can be described using four structural lipoprotein, the remaining moleculeis calledan apolipoprotein. categories: primary, secondary, tertiary, and quaternary. Primary Proteins can also be categorized by shape into two major structure is determined by the sequence of amino acids in the groups: globular and fibrous. Globular proteins are compact, polypeptide chain, the identity and specific order of the amino folded, and coiled chains that are relatively soluble. The hydro-phobic acids. This sequence is found in the genetic DNA coding, as dis-cussed groups are folded within the protein, and the hydrophilic later in this chapter. Peptide bonds are the primary bonds groups are on the outer surface. The ratio of length to breadth between atoms in the primary structure, and the molecule is (L/B) is less than 10. Most serum proteins are globular, which are one-dimensional. compact, without space for water in the inner core containing the Secondary structure is determined by the interaction of hydrophobic molecules. Fibrous proteins are structural proteins adjacent amino acids. The winding of the polypeptide chain, the including hair, keratin, collagen, troponin, and fibrin. The ratio of formation of hydrogen bonds between the NH and CO groups length to breadth (L/B) is greater than 10. Fibrous proteins are of the peptide bonds, and the occasional disulfide bonds affect insoluble in water or saline. its secondary structure. It is the regular, recurring arrangement of the primary structure in one dimension. Denaturation Three possible conforma-tionsa@helix, b@pleated sheets, and random coilsare illustrated Denaturation is the disruption of the bonds holding the sec-ondary, in Figure 9-3. Secondary structure remains one-dimensional. tertiary, or quaternary structures together, but it does Tertiary structure is the way in which the chain folds back not affect the primary structure and does not break the peptide upon itself to form a three-dimensional structure. The bonds bonds. Hydrolysis is catalyzed by acid, base, or digestive enzymes responsible for this structure are covalent bonds, for example, and does break peptide bonds. If the bonds are broken, the poly-peptide disulfide bonds, and noncovalent bonds such as hydrogen, hydro-phobic, chains unfold or their quaternary structure is lost. This electrostatic, and Van der Waals.Theseare mainlyinterac-tions results in the loss of activity and also the functional and structural of amino acids with the R-groups of more distant amino characteristics of the protein molecule. Denaturation can occur acids. Tertiary structure determines the chemical and physical as a result of heat, changes in pH, mechanical forces, exposure properties of the protein. to chemicals (solvents, detergents, metals), and exposure to ultra-violet Quaternary structure is the arrangement of two or more light. The bonds holding the quaternary and tertiary struc-tures polypeptide chains to form a protein. Only proteins with more together are weak, and if they are destroyed, proteinsfor than one polypeptide chain have quaternary structure. The num-ber example, enzymeswill lose their activity. of polypeptide chains and type (identical or different) deter-mine the specific properties of the complex. For example, creatine kinase is an enzyme that is dimeric, that is, it consists of two poly-peptide CHeCKPOINT! 9-1 chains, M or B, resulting in three possible combinations: 1. Define amphoteric. MM, MB, and BB. Proteins are classified into two major groupssimple proteins 2. At a pH above its isoelectric point, a protein carries a and conjugated proteins. Simple proteins are those composed (positive or negative) charge. only of amino acids, for example, albumin. Conjugated proteins 3. In a protein with three polypeptide chains, the chains are proteins that have nonprotein groups attached to them, provid-ing are arranged to forms its structure. certain characteristics to the protein. Metalloproteins have a 4. Conjugated proteins that contain cholesterol and tri-glycerides metal ion attached to the protein, like ceruloplasmin, which has are called. copper. Lipoproteins contain lipids such as cholesterol, triglycer-ides, and phospholipids. Glycoproteins are compounds consisting PROTEIN METABOLISM Digestion of dietary proteins by proteolytic enzymes originates in the gastrointestinal tract. Amino acids are released and absorbed in the jejunum and transported through the portal circulation system to amino acid pools, where they are stored. The amino acid pools are especially important in conserving the essential amino acids discussed earlier. The liver and other organs utilize the amino acid A-helix b-pleated sheets Random coil pools to synthesize the bodys proteins, as described in the follow-ing FIGURE 9-3 Secondary structure of proteins. section 218 Chapter 9 amino aCids and proteins In the kidneys, amino acids are filtered through the renal glomeruli but are subsequently reabsorbed by the renal tubules. BOX 9-1 Protein Functions Although the details of the process of reabsorption are not known, Maintenance of colloidal osmotic pressure and water it is an active transport system that is based on membrane-bound distribution carriers and intraluminal Na+ concentration. Increased plasma lev-els Structuralsupport for the body, tissue, or cell of amino acids, as occur in aminoacidopathies, covered later in this chapter, result in increased renal excretion of amino acids. Collagen Keratinhair, nails Transport molecule; for example, PROTEIN SYNTHESIS Transferrin@Fe+3 Most plasma proteinsexcept for immunoglobulins (antibodies), Albumin-bilirubin some coagulation factors, protein hormones, and hemoglobinare Thyroid binding globulins synthesized in the liver and secreted into circulation by the Hormones hepatocytes. Hepatocytes synthesize many proteins simultaneously Enzymes and balance synthesis with degradation, which is occurring at the Peptide hormones, insulin same time. This balance maintains plasma protein levels within a Coagulation fairly narrow range. The primary structure or sequence of amino acids is deter-mined Hemoglobin by the sequence of purine and pyrimidine (adenine, guanine, Antibodies cytosine, and pyrimidine) bases in the DNA molecule, which code for the particular protein. The double-stranded DNA molecule unfolds and one strand serves as a template for the messenger RNA transported by protein are iron carried by transferrin, bilirubin (mRNA). The information on the mRNA also has the initiation and linked to albumin, and thyroid hormones bound to thyroxine-binding termination codes to begin and end the specific protein molecule. globulin (TBG). Peptide hormones, for example, insulin, The code is carried by the mRNA from the nucleus to the serve critical functions in the body. Hemoglobin, the major pro-tein cytoplasm of the cell, where it attaches to a ribosome receptor in red blood cells, carries oxygen throughout the body. Immu-noglobulins protein on the ribosome. The code contains codons, or sequences (antibodies) are very important constituents of the of three bases specific for a particular amino acid. The next step bodys immune system.1 See Box 9-1 for a list of protein functions. in the processis getting the amino acids in the genetic code to the mRNA. The amino acid linked to another RNA, called transfer AMINOACIDOPATHIES RNA (tRNA), that corresponds to the specific codon is carried to the ribosome and is attached to the matching codon. The free Aminoacidopathies are inherited disorders of amino acid metabo-lism. tRNA returns to the cytoplasm, where it can bind to another amino The disorder can be a specific enzyme in the metabolic path-way acid. The next amino acid in the sequence is added and the cycle or in the membrane transport system for amino acids. Over repeats itself until the protein is completed when the terminal 100 aminoacidopathies have been identified, including alkapton-uria, codon is reached. When this occurs, the mRNA and the ribosome cystinuria, phenylketonuria, and maple syrup urine disease, dissociate. The proteins are then secreted into the space of Disse which we will focus on in this chapter. and move through the hepatic sinusoids into the bloodstream. Alkaptonuria Alkaptonuria is a rare inherited disease involving the homogen-tisic PROTEIN FUNCTIONS acid oxidase (HGO) gene that results from the deficiency Proteins serve many functions in the body. One of the major of the enzyme homogentisic acid oxidase in the catabolic pathway roles is maintenance of water distribution between cells and tis-sue. of tyrosine. The incidence of the disease in the general population When protein levels are decreased, the osmotic pressure is also is about 1:250,000. This deficiency leads to a buildup of homo-gentisic decreased, allowing more water into the interstitial fluid, resulting acid (HGA) in the tissues of the body. It is an autosomal in edema. Plasma colloidal osmotic pressure (COP) provided by recessive condition, which means both parents have one normal the proteins tends to retain water in the vascular space. Structural gene and one alkaptonuric gene that they pass on to their offspring.2 proteins also provide support for the body, tissues, or cells. Keratin, Ochronosis, one of the characteristics of alkaptonuria, is found in nails and hair, and collagen are examples of two structural the darkening of the tissues of the body because of the excess proteins. Collagen is a strong, fibrous, insoluble protein found in homogentisic acid in alkaptonurics. This occurs later in the disease, connective tissue and makes up about 25% of the bodys weight. usually when patients are in their 40s, when the pigments accumu-late Proteins also function as enzymes (biological catalysts). and cause slate blue, gray, or black discoloration of the carti-lage Coagulation proteins are important in maintenance of hemo-stasis in the joints and ears, skin, and sclerae (whites) of the eyes. It or blood coagulation. Many proteins function as transport also causes bluish discoloration of the nails in some patients. The vehicles to move various ligands (an ion or molecule that reacts deposition in joints can lead to arthritis like degeneration of the to form a complex bond with another molecule) to where they large joints (hips) as well asintervertebral discs at the thoracic and are needed or stored in the body. Examples of molecules that are lumbar levels, leading to back pain.  Chapter 9 amino aCids and proteins 219 One of the earliest signs of the disorder is the tendency for a synthetic formula or medical food that provides all essential diapers to stain black due to the oxidation of HGA in the urine. nutrients and all amino acids except leucine, isoleucine, and valine. Homogentisic acid can be identified in the urine, using gas chro-matography These are added in very controlled amounts to provide the neces-sary and massspectroscopy(GC-MS).2 levels for normal growth and development without exceeding Alkaptonuria is a slow, progressive disorder that is irreversible. levels that would lead to a buildup of these amino acids. The diet Treatment focuses on preventing the complications of the condition, requires lifelong restriction of branched-chain amino acids.6 for example, arthropathy. Avoiding a diet high in protein, phenylala-nine, and tyrosine is thought to reduce or minimize complications Phenylketonuria later in life. Patients with alkaptonuria havea normal lifespan.2 Phenylketonuria (PKU) is another inborn error of metabo-lism that results in the inability to metabolize the essential amino Csytinuria acid phenylalanine. It is an autosomal recessive trait, occurring in Cystinuria is not a metabolic enzyme deficiency but a defect approximately 1:14,000 to 1:20,000 births in the United States. The in the amino acid transport system. Normally, amino acids are biochemical defect is a deficiency of the enzyme phenylalanine freely filtered by the renal glomeruli and then actively reabsorbed hydroxylase (PAH) that converts phenylalanine to tyrosine.2 by the proximal convoluted tubules. In patients with cystinuria, PKU screening on dried blood on a filter paper by tandem cystine as well as other diamino acids, including lysine, arginine, MS/MS is one of the mandatory tests performed on newborns. and ornithine, are excreted in significant amounts. They are not Classic PKU is diagnosed when phenylalanine levels exceed reabsorbed and the concentration excreted in urine is increased 20 mg/dL without treatment. Other characteristics of PKU are 20 to 30 times normal. Cystine, however, appears to cause the a mousy urine odor due to the breakdown products of phenyl-alanine, most problems.4 including phenylpyruvic acid, found in the urine; eczema; Cystine is somewhat insoluble, resulting in its precipitation seborrhea; and fair coloring due to the tyrosine deficiency that in the renal tubules and the formation of urinary calculi (kidney subsides with age.7 stones). Symptoms suggestive of kidney stones may result in the Pregnant women known to be carriers of the PKU gene or diagnosis of cystinuria. Patients report flank pain or pain in the definitely carrying a PKU fetus should also be maintained on a side or back, which may be progressive, getting increasingly worse, phenylalanine-restricted diet from conception to birth. Studies andit mayradiate to the lower flank, pelvis, groin, or genitals.5 The have reported that women who followed a normal diet while car-rying urinalysis mayalsoindicate blood in the urine. a PKU fetus always delivered a baby who was microcephalic Increased fluid intake (a minimum of 6 to 8 glasses of water and mentally retarded. per day) and alkalizing the urine with potassium citrate, sodium Elevated phenylalanine levels are toxic to developing brain citrate, or other medications will help prevent the formation of tissue and negatively impact brain function. If not diagnosed early, kidney stones. Penicillamine may also be used to increase the solu-bility patients with PKU are usually mentally retarded, but the affect of of cystine. This is a chronic, lifelong condition, but it is not PKU can be controlled through dietary treatment.7 If appropriate life threatening and does not affect other organs. treatment is initiated early, the patients IQ should be within 58 points of his or her siblings. The most important treatment is phenylalanine restriction and MapleSyrup Urine Disease supplementation of diet with essential amino acids, minerals, and Maple syrup urine disease (MSUD) is named for the character-istic vitamins. Aspartame, one of the primary sweeteners in foods maple syrup or burnt sugar odor of the urine of persons with and soft drinks, also should be avoided. Formerly, the diet was this condition. MSUD is caused by the absence or very low levels discontinued at 5 or 6 years of age, but it has now been determined of the branched-chain enzyme a@ketoacid decarboxylase complex, that slight brain damage occurs after the discontinuation of the which results in the abnormal metabolism of three essential amino diet, and most physicians no longer recommend suspending the acids: leucine, isoleucine, and valine. These are converted to toxic program. ketoacids that cannot be oxidized, leading to their accumulation in the serum, urine, and spinal fluid.2 The first symptoms of MSUD in the newborn are poor CHeCKPOINT! 9-2 appetite, lethargy, irritability, irregular sleep patterns, and the char-acteristic 1. Most plasma proteins are synthesized in the. odor of the urine. MSUD should be considered when 2. List three major protein functions. an infant presents with severe acidosis within the first 10 days of life, and screening should be done 12 hours after birth or later. 3. Identify the aminoacidopathy associated with the Infants also lose their sucking reflex and become listless, have a following: high-pitched cry, and become limp, with episodes of rigidity. If a. ochronosis treatment is not initiated quickly, the symptoms progress rapidly to b. mousy urine odor seizures, coma, and death. It is usually lethal within the first month c. formation of kidney stones of life if unrecognized and untreated. The earlier the diagnosis and treatment, the lower the risk of permanent damage.6 d. deficiency of homogentisic acid oxidase Treatment involves a special, very carefully controlled diet e. deficiency of a@ketoacid decarboxylas requiring careful monitoring of protein intake. It centers around 220 Chapter 9 amino aCids and proteins SPECIFICPLASMA PROTEINS BOX 9-2 Functions of Albumin Proteins are categorized into two main groups: albumin and globulin. Globulins are divided into four groups: a1@globulins, *Maintain plasma colloidal osmotic pressure a2@globulins, b@globulins, and g@globulins. Some of the major Bind and transport a wide variety of ligands proteins under each class will be reviewed. Bilirubin Long chain fatty acids Prealbumin/Transthyretin Therapeutic drugs (e.g., warfarin, diazepam, Prealbumin or transthyretin (TTR) binds with thyroxine, tri-iodothyronine digoxin, phenylbutazone, salicylate, penicillin) (thyroid hormones), and retinol (vitamin A) and Calcium serves as a transport protein. It is a nonglycosylated, tetrameric Magnesium serum protein consisting of four identical subunits of 127 amino Hormones (e.g., thyroxine, triiodothyronine, acids each, which are synthesized in the liver, and the choroid cortisol) plexus of the brain. Prealbumin is rarely seen on cellulose acetate Serve as an endogenous source of amino acids electrophoresis and is more likely detected in high-resolution elec-trophoresis Acid base balance (HRE).8 Pro-and anti-coagulatory effects The main clinical significance of prealbumin is its role as a sensitive marker of poor nutritional status such as protein-energy *Chief biological function malnutrition (PEM). Decreased prealbumin indicates dietary intake of protein is not adequate, resulting in decreased synthesis of prealbumin by the liver. People at risk for PEM are the elderly and those who are hospitalized or in a nursing home. Impaired or decreased synthesis can be divided into two catego-ries: Chronic illnesses (diabetes, arthritis), increased nutritional losses, primary, associated with liver disease, and secondary, due to open wounds, burns, and malabsorption (gastrointestinal protein-losing diminished protein intake, malabsorption, or malnutrition. The diseases) are other causes of protein-energy malnutrition. third category is increased protein loss, which is mainly renal. See Prealbumin is also decreased in acute inflammatory response Box 9-3 for more detail. (acute phase reactant, APR), liver disease, nephrotic syndrome, Hyperalbuminemia is of little diagnostic significance except and other protein-losing renal diseases. If undiagnosed, protein-energy in dehydration. The increase in albumin is usually artifactual due malnutrition can lead to increased risk of morbidity and to a decrease in plasma volume; as a result, normal albumin levels mortality.8 are diluted in a larger volume of plasma. Prealbumin has a high ratio of essential-to-nonessential amino acids, making it a sensitive indicator of the quality of protein intake. It can detect PEM earlier because of its short half-life of 2 to 8 days. Prealbumin methodologies include immu-nonephelometry, MINI CASE 9-1 immunoturbidimetry, and radial immunodiffu-sion. The reference range for transthyretin is 150350 mg/L; for nancy, a 62-year-old woman, was admitted to the increased risk of malnutrition, 110150 mg/L; for significant hospital with confusion, weakness, dehydration, and risk, 50109 mg/L; and for poor prognosis, 650 mg/L.8 congestive heart failure. She had lost 29 pounds over the previous six months. She had been unable to take Albumin any oral nutrition during the three to five days prior to Albumin is synthesized in the liver and comprises approximately admission. 60% of total serum protein. The rate of synthesis is dependent on Her albumin level was suboptimal at admission. Per-cutaneous protein intake and is subject to feedback regulation by the plasma endoscopic gastrotomy (PEG) tube feeding albumin level and plasma colloidal osmotic pressure (COP). The was initiated and she was stabilized and began taking an chief biological function of albumin is to maintain plasma COP. adequate amount of nutrition orally. The high concentration of albumin makes up approximately 80% The laboratory findings were: of the total pressure, which keeps intravascular fluid inside the Protein: 5.5 g/dL (6.08.4 g/dL) blood vessels and out of the interstitial fluid, which would result Albumin: 3.0 g/dL (3.55.0 g/dL) in edema.9 Anotherfunction of albuminis to transport and store Transthyretin (prealbumin): 115 mg/L (150350 mg/L) a wide variety of ligands, such as bilirubin, listed in Box 9-2. A ligand is an ion or molecule that reacts to form a complex with 1. What condition does nancys profile suggest? another molecule. 2. What risk category do the transthyretin (prealbumin) The most common cause of decreased albumin levels, hypoal-buminemia, results indicate? is increased catabolism due to tissue damage and inflam-mation. 3. What is her A/G ratio? Is it elevated, within the refer-ence The liver is too busy synthesizing proteins to repair the range, or decreased body; therefore, it is unable to keep up with albumin production.  Chapter 9 amino aCids and proteins 221 (e.g., cirrhosis and hepatocellular carcinoma in children and adults). BOX 9-3 Hypoalbuminemia Pulmonary emphysema is the major cause of disability and death; however, liver cirrhosis and/or cancer are present in 3040% of *Increased catabolism: tissue damage and inflammation patients over age 50 with AAT deficiency.12Increasedlevels of Impaired or decreased synthesis AAT are present in inflammatory reactions (APR), pregnancy, and Primary: liver disease women on estrogen. Secondary: diminished protein intake, malnutrition, Quantitative assays, including immunoturbidimetry and immu-nonephelome malabsorption are available to determine levels of AAT that Increased loss of protein have a reference range of 100300 mg/dL. They do not, however, nephrotic syndrome provide information on the particular genetic defect responsible Chronic glomerulonephritis for the deficiency. Detection of AAT deficiencies is critical because Diabetes mellitus/diabetic nephropathy effective replacement therapy is available and treatment should be Extensive burns initiated as early as possible.12If the level is below 50 mg/dL, a Acute viral gastroenteritis phenotyping should be performed to classify the specific genetic defect. Genetic defects (Pi, Z, or null phenotypes) are beyond the *Most common cause scope of this book and the reader is referred to the references at the end of the chapter. GLOBULINS A1@AcidGlycoprotein (Orosomucoid) A1@acid glycoprotein (AAG) is the major glycoprotein increased a1@Globulins during inflammation (APR). It was one of the first glycoproteins A1@Antitrypsin to be isolated in its pure state. It is the primary carrier of basic A1@antitrypsin (AAT) is the major a1@globulin making up approx-imately (positively charged) drugs, whereas albumin carries the negatively 90% of a1 proteins. AAT is a glycoprotein synthesized by charged acidic drugs. Elevated levels are found in rheumatoid the liver and released into the plasma. It is an acute phase reac-tant arthritis, stress, cancer, acute myocardial infarction, pneumonia, (APR) with antiprotease activity, resulting in neutralizing leu-kocyte surgery, and other conditions resulting in an increased APR.13 elastase and collagenase. Levels may double in acute and chronic infections and other conditions resulting in the release of Alpha-Fetoprotein APRs. AAT deficiency, one of the most common genetically lethal Alpha-fetoprotein (AFP) is the first a1@globulin from the fetus diseases in Caucasians (1:4000), is associated with lung and liver to appear in the mothers serum during pregnancy. AFP is the prin-cipal disease.10 fetal protein (fetal albumin-like protein) in maternal serum AAT is one of a family of serum proteins called serpins (ser-ine used to screen for the antenatal diagnosis of neural tube defects, proteinase inhibitors). AAT deficiency is a genetic inherited including spina bifida and anencephaly. Spina bifida is a congeni-tal autosomal dominant condition caused bythe mutationin the SER-PINA1 defect in the walls of the spine that allows a protrusion of the gene located in the long arm of chromosome 14. Examples spinal cord or meninges. Anencephaly is the congenital absence of other proteins in this group are a1@antichymotrypsin and anti-thrombin. of the brain or cranial vault, resulting in a disorganized mass of AAT is actually a misnomer. Although 90% of antitryp-sin neural tissue. These conditions allow increased passage of fetal activity is attributed to AAT, plasma contains very little trypsin, protein into amniotic fluid and indicate fetal distress. AFP is also and most of the AAT function is to inhibit nonprotein proteinases, increased in some abdominal wall defects in the fetus.14 especially collagenase and elastase. Alpha-fetoprotein levels peak in the fetus at 13 weeks ges-tation AAT deficiency is found in 15% of patients with chronic (end of the first trimester) and decrease at 34 weeks. In obstructive pulmonary disease. It is related to early onset emphy-sema maternal serum, the level peaks at 30 weeks gestation. Screening is because particles and bacteria are continually removed usually performed at 16 to 18 weeks gestation, and normal levels from the lungs by polymorphonuclear neutrophils (PMNs) that are determined using such variables as the weight of the mother, release elastase. Normally, sufficient AAT is present to bind the the race of the mother (higher in African Americans), presence free elastase released from the neutrophils. If AAT levels are not of type 1 diabetes mellitus, and multiple births. For example, if adequate, proteases, including elastase from the neutrophils, attack the mother is having twins or triplets, the AFP would increase lung tissue. Elastase reacts with elastin in the vascular endothe-lium, proportionally. destroying the lung tissue. AAT is very important in preven-tion Multiple of the median (MoM) is calculated by dividing the of loss of elastin lung recoil, which results in emphysema. patients AFP by the median reference value for the gestational Emphysema with onset at 45 years of age or earlier and emphy-sema age. Elevated AFP leading to incorrect interpretation of the MoM occurring in the absence of smoking are common features can be caused by fetal demise, incorrect gestational age, multiple of AAT deficiency. The most common symptoms are dyspnea on fetuses, and fetomaternal bleeds. exertion, wheezing, cough, and chronic bronchitis.11 Alpha-fetoprotein is decreased in Downs syndrome and Tri-somy Although AAT deficiency is associated with early onset 18. AFP can also be used as a tumor marker, with increased emphysema, a congenital deficiency can also result in liver disease levels found in testicular and ovarian (nonseminoma) carcinom 222 Chapter 9 amino aCids and proteins and hepatocellular carcinoma. Elevated AFP has also been found Ceruloplasmin in the serum of patients with benign liver disease and gastrointes-tinal Ceruloplasmin (Cp) is the principal copper (Cu)-containing pro-tein tract tumors.15 in plasma,comprising 95% of the total serumcopper.It is not, however, atransport protein (it does not gain orlose copper), butit A1@Antichymotrypsin doesprevent coppertoxicity. It is nowthought that Cpplaysarole A1@antichymotrypsin (ACT) is an APR serum glycoprotein that in copper metabolism by releasing copper to key copper-containing belongs to a class of serine protease inhibitors (serpins) that cata-lyze enzymes. The primary role of Cp seemsto bein plasma redox reac-tions, chymotrypsin, pancreatic elastase, and mast cell chymase. ACT andit can bean oxidant or antioxidant, dependingon various is found between the a1 and a2 zones. It is elevated in inflamma-tion factors such asthe presence of ferric ions and ferritin-binding sites. and indicates APR protein synthesis. Decreased levels of ACT For example, Cp oxidizes Fe+2to Fe+3,allowing incorporation of are associated with asthma, chronic obstructive pulmonary disease, iron into the transferrin moleculewithoutthe formation of toxic and liver disease. ACT has also been found to be an integral com-ponent products. Cp does play a role in preventing lipid oxidation and free of the amyloid plaquesin Alzheimers patients.16 radical formation, which is damaging to cells. Althoughcopperis an essentialnutrient,it is verytoxic to cells a2@Globulins in high concentrations. The primary storage site is the liver, and Haptoglobin the principal site of excretion is the biliary tract. Ceruloplasmin Haptoglobin (Hp) is an a2@globulin and an acute phase reactant binds mostof the copper releasedinto plasma. Cp carries 6to and the primary protein that binds free hemoglobin in plasma. It 8 Cu atoms per apoceruloplasmin that are half cuprous (Cu+) and consists of two nonidentical chains, a and b [(ab)2], linked by half cupric (Cu+2). Pure Cp has a blue color. Copper homeostasis disulfide bonds, and its primary function is irreversible binding is basedon the balance betweenabsorption in the intestine and with the a@chains of the globin portion of free oxyhemoglobin excretion in the biliary tract. A, F, S, and C in plasma. The complex is then removed from Wilson disease (WD) is a rare autosomal recessive trait the plasma within minutes by the mononuclear-phagocyte sys-tem whereCplevels arereducedandthe dialyzableCuconcentrationis (spleen, thymus, lymph nodes), where the components are increased. A mutationin the gene for a copper-transporting ATPase metabolized to free amino acids and Fe within hours. Haptoglobin (ATP7B) results in decreased movement of copper into bile and prevents loss of hemoglobin through the renal glomeruli. Approxi-mately accumulation of copperin the liver and other tissues. Thisenzyme 1% of red blood cells are removed from circulation each is also responsible for ensuring apoceruloplasmin hasits full com-plement day, and the body normally synthesizes enough Hp to take care of of copper. Patients usually develop symptoms in their 20s a normal load. Hps primary function was originally thought to be or 30s,althoughit maybe earlier or later. Excessiveaccumulation the preservation of iron and prevention of renal tubular damage of Cuin the liver, kidney, and brain can lead to degenerative cirrho-sis, by hemoglobin excretion. However, another important role of Hp chronic active hepatitis, renal tubular acidosis, and neurologi-cal is the control of local inflammatory response through a number of damage(clumsiness,tremors, uncontrolled movements)unless processes. For example, the Hp-hemoglobin complex is a complex treated with a copper chelator. Although the incidence of WDis peroxidase that can hydrolyze peroxidases released during phago-cytosislow, it is one of the morecommon causesof chronicliver disease and catabolism by polymorphonuclear leukocytes at the in children. Copper also depositsin the eyes,resulting in the charac-teristic site of inflammation. It is also a natural bacteriostatic agent in Kayser-Fleischer rings, pigmented rings atthe outer margins infections with iron-requiring bacteria, for example, Escherichia coli. of the corneaandthe sclera.In othertissues,excessivecopper can Hp depletion is the most sensitive indicator of intravascu-lar causerenal tubular damage, kidney stones, osteoporosis, arthropa-thy, hemolysis (hereditary spherocytosis, autoimmune hemolytic cardiomyopathy, and hypoparathyroidism.18 anemia) and extravascular hemolysis. In transfusion reactions and Diagnosisof Level1 WDis definedaslow serum ceruloplas-min certain hemolytic disorders (hemolytic anemias), Hp levels are not (620 mg/dL) andthe presenceof Kayser-Fleischerrings. If sufficient to take care of the increased load and Hp is decreased. treated before the onset of cirrhosis and neurological symptoms, Hp levels are also decreased in severe burns, acute and chronic patientscanlead a normallifespan. Trientine(Syprine) and penicil-lamine hepatocellular disease (cirrhosis), pregnancy, and disseminated can be used to chelate copper and promote its excretion in intravascular coagulation(DIC).17 Epstein-Barr and cytomegalo-virusthe urine. Because WDis an autosomal recessive trait, following infections and high estrogen levels (oral contraceptives or diagnosisallsiblings and parents siblings should bescreened. pregnancy) may result in low levels of Hp. RBC destruction dur-ing Increased levels are also detected during pregnancy and in strenuous exercise also can cause a temporary decrease in Hp. women on oral contraceptives. Cpis an acute phase reactant that Haptoglobin is an APR that is synthesized late and weak increaseslate in the conditionacute and chronic infections,lym-phoma, reacting. As with all APRs, Hp is increased in conditions involv-ing and rheumatoid arthritis. Decreasedlevels are found in inflammation (infection, trauma, hepatitis, leukemia), increased liver disease because of impaired synthesis, malnutrition, intestinal estrogen level, diabetes mellitus, smoking, nephrotic syndrome, tis-sue malabsorption,and conditions resulting in increased proteinloss necrosis, or malignancy.17 (nephrotic syndrome).19 Haptoglobin can be measured byimmunochemical methods, Cp can be measured by immunonephelometry, immuno-turbidimetry, including immunonephelometry and immunoturbidimetry. The or radial immunodiffusion. The referencerange is reference range is 30200 mg/dL. 2035 mg/dL  CHAPTER 9 Amino ACids And PRoTEins 223 A2@Macroglobulin methods, including immunonephelometry and immunodiffu-sion, A2@macroglobulin (AMG) is one of the largest plasma proteins, and indirectly with total iron-binding capacity (TIBC). TIBC consisting of four identical subunits that are actually two dimer (mg/dL) * 0.70 willgivean approximate concentration of trans-ferrin subunits. AMG is a protease inhibitor that inhibits trypsin, pepsin, (mg/dL). The transferrin saturation can be calculated by thrombin, and plasmin. Although it appears to be an important (serumiron level * 100) , TIBC. Thereferencerangein adults antiproteinase, plasma concentrations of AMG are only 1/10 is 2050% and more than 16% in children. those of AAT. AMG is involved in the primary or secondary inhi-bition of enzymesin the complement, coagulation, and fibrinolytic Hemopexin pathways. Hemopexin is another plasma glycoprotein along with haptoglo-bin In nephrotic syndrome, AMG is characteristically increased up that removes heme from circulation. When red blood cells to 10 times normal because it is retained, whereas smaller proteins are destroyed, hemopexin transports heme to the liver, where it is are excreted in the urine. Increased synthesis of all proteins, includ-ing catabolized by the reticuloendothelial system. It also removes heme AMG, by the liver to compensate for the urinary loss of smaller from the breakdown of myoglobin or catalase. proteins also contributes to the elevation. a2@macroglobulin is also Hemopexin is similar to haptoglobin in being a positive but elevated in liver disease (hepatitis, cirrhosis) and women on estro-gen weak APR. Increased levels are found in inflammation, pregnancy, (oral contraceptives or hormone replacement therapy (HRT)), and diabetes mellitus. Decreased levels are found in some malig-nancies and slightly increased in diabetes mellitus. Decreased levels are and Duchenne-type muscular dystrophy. Low hemopexin associated with pancreatitis, rheumatoid arthritis, and multiple levels are found in a variety of hemolytic diseases including hemo-lytic myeloma.20 anemias, sickle cell anemia, paroxysmal nocturnal hemoglo-binuria, Immunonephelometry, enzyme-linked immunoassay (ELISA), and thalassemia major. and radial immunodiffusion assays for AMG are available, although of very limited clinical use. The reference range for AMG is 100280 B@Lipoproteins mg/dL. B2@lipoproteins are a class of lipoproteins that travel with the b@globulins. Lipoproteins are complexes of proteins and lipids whose function is to carry lipids in the plasma. b@lipoproteins are b@Globulins classified aslow-density lipoproteins (LDLs), which transport the Transferrin majority of cholesterol in the body from the liver to the tissues. Transferrin (TRF) is the major component of b@globulins and High levels of LDLs are a risk factor for atherosclerosis and the principal plasma protein for transport of iron (Fe+3ferric heart disease, and is covered in Chapter 8 Lipids and Lipoproteins. ion) from the intestine, where it is absorbed by apotransferrin, to Elevated LDLs are also seen in nephrotic syndrome, hepatobiliary red cell precursors in the bone marrow, or to the liver, bone mar-row, disease, diabetes mellitus, and hypothyroidism. or spleen for storage. TRF transports iron to storage sites, where it is bound to apoferritin and stored as ferritin. It also pre-vents B2@Microglobulin excretion of Fe through the kidney. B2@microglobulin (BMG) is a protein on the cell membrane Adults have 35 grams of body iron; however, only 0.1% or of most nucleated cells and is found in especially high levels in 3 mg circulates in the plasma bound to transferrin. Each transfer-rin lymphocytes. BMG is alow molecular weight protein that com-prises molecule can carry two ferric ions, but normally only one-third the common light chain of Class I major histocompatability of the sites are occupied. TRF is responsible for most of the total complex (MHC) antigens found in all nucleated cells. It is a small iron-binding capacity of plasma. protein that is filtered bythe renal glomeruli but is reabsorbed and Transferrin is important in the differential diagnosis of ane-mias catabolized by the proximal convoluted tubules. and in monitoring the treatment of iron deficiency anemia b2@microglobulin is increased in renal failure, inflammation, when the transferrin level is increased, but the percent satura-tion and neoplasms, especially those associated with b@lymphocytes. is decreased. Increased TRF levels have been associated with The plasma level of BMG is a good indicator of the glomerular increased morbidity and mortality with cirrhosis, hepatitis, diabetes filtration rate. It is used primarily to test for renal tubular function mellitus, and cardiomyopathy.21 It is a negative acute phase reac-tant, in renal transplant patients when decreased renal tubular function with low levels occurring in inflammation and malignancy as indicates early rejection.23 well as nephrotic syndrome and hemochromatosis. TRF levels are BMG elevations are also associated with a number of lym-phoproliferat also decreased in starvation, anorexia, and malnutrition and can disorders such as multiple myeloma, malignant serve asa markerof protein-energy malnutrition(PEM).22 lymphomas, and chronic lymphocytic leukemia. Values have been Serum transferrin is commonly used as an indicator for iron shown to correlate with prognosis. In multiple myeloma, serum overload, and a frequent first step in screening for hemochro-matosis, values of 64 mg/mL wereassociated with significant increasein a hereditary disorder involving excessive absorption and survival.23 Inflammatory conditions such as hepatitis, rheumatoid accumulation of iron in the body. Hemochromatosis is character-ized arthritis, systemic lupus erythematosus (SLE), and acquired immu-nodeficiency by bronze skin, cirrhosis, arthritis, and congestive heart failure. syndrome (AIDS) are also associated with elevated The reference range for transferrin is 240450 mg/ BMG. The elevation of BMG in these conditions may be due to dL. TRF can be measured by various immunochemical increased lymphocyte turnover  224 Chapter 9 amino aCids and proteins BMG can be measured by enzyme immunoassay, with an of complement activation. Third, the terminal complement com-ponents upper limit of 1.212.70 mcg/mL in serum. damage certain bacteria by creating pores in the bacterial membrane.26 Onceactivated, the complement cascade results in C-Reactive Protein lysis of the cell. C-reactive protein (CRP) is an acute phase reactant and a non-specific Complement proteins, especially C3 and C4, are acute phase indicator of bacterial or viral infection, inflammation, and reactants (APRs) and increase in inflammatory states. They are, tissueinjury or necrosis.It is called C-reactive becauseit wasfirst however, late reacting and weak. C3 and C4 are also elevated in discovered in the serum of patients with Streptococcus pneumoniae biliary obstruction. Variant and genetic deficiencies of C2 and infections resulting in precipitation with C-substance, a polysac-charide C4 are associated with autoimmune disorders, immune complex of Streptococcus pneumoniae. CRPreacts with proteins present diseases including lupus erythematosus, and glomerulonephritis. in many bacteria, fungi, and protozoal parasites. C3 deficiencies are found in pyogenic infections, particularly with CRP is composed of five identical subunits, nonglycosyl-ated encapsulated bacteria, especially meningococci.27 Decreasedlevels polypeptides, synthesized in the liver. When CRP is bound are found when the coagulation proteins have been consumed or to bacteria, it activates complement, neutrophils, and monocyte-macrophages used up, such as disseminated intravascular coagulation or parox-ysmal and leads to phagocytosis. These all play a role in nocturnal hemoglobinuria, and in conditions when the body CRPs recognition of microorganisms and its role as an immu-nomodulator cannot produce adequate proteins, for example, malnutrition. in the bodys defense