Proteins & Amino Acids PDF

Proteins and Amino Acids © 2010 Pearson Education, Inc. What Are Proteins? Large molecules Made up of chains of amino acids Are found in every cell in the body Are involved in most of the body’s functions and life processes The sequence of amino acids is determined by...

Proteins and Amino Acids © 2010 Pearson Education, Inc. What Are Proteins? Large molecules Made up of chains of amino acids Are found in every cell in the body Are involved in most of the body’s functions and life processes The sequence of amino acids is determined by DNA © 2010 Pearson Education, Inc.  What are Protiens ?  Proteins are a sequence of amino acids  One amino acids is joined to the next by a PEPTIDE bond  Provide energy substrate for metabolism (4 kcals/g).  Protein load received by the gut is derived from two primary sources: 70-100 g dietary protein, and 35-200 g endogenous protein, © 2010 Pearson Education, Inc. Structure of Proteins Made up of chains of amino acids; classified by number of amino acids in a chain Peptides: fewer than 50 amino acids - Dipeptides: 2 amino acids - Tripeptides: 3 amino acids - Polypeptides: more than 10 amino acids Proteins: more than 50 amino acids - Typically 100 to 10,000 amino acids linked together Chains are synthesizes based on specific bodily DNA Amino acids are composed of carbon, hydrogen, oxygen, and nitrogen © 2010 Pearson Education, Inc. Structural Differences Between Carbohydrates, Lipids, and Proteins Figure 6.1 The Anatomy of an Amino Acid Figure 6.2b Peptide Bonds Link Amino Acids Form when the acid group (COOH) of one amino acid joins with the amine group (NH2) of a second amino acid Formed through condensation Broken through hydrolysis © 2010 Pearson Education, Inc. Condensation and Hydrolytic Reactions Figure 6.3 Essential, Nonessential, and Conditional Essential – must be consumed in the diet Nonessential – can be synthesized in the body Conditionally essential – cannot be synthesized due to illness or lack of necessary precursors Premature infants lack sufficient enzymes needed to create arginine © 2010 Pearson Education, Inc. Structure of the Protein Four levels of structure Primary structure Secondary structure Tertiary structure Quaternary structure Any alteration in the structure or sequencing changes the shape and function of the protein © 2010 Pearson Education, Inc. Denaturing Alteration of the protein’s shape and thus functions through the use of Heat Acids Bases Salts Mechanical agitation Primary structure is unchanged by denaturing © 2010 Pearson Education, Inc. Denaturing a Protein Figure 6.5 Quick Review Proteins are chains of combination of amino acids Amino acids contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur Unique amino acids consist of a central carbon with a carboxyl group, a hydrogen, a nitrogen-containing amine group, and a unique side chain There are 20 side chains and 20 unique amino acids 9 essential amino acids 11 nonessential amino acids - At time these become conditionally essential Amino acids link together with peptide bonds by condensation and break apart by hydrolysis © 2010 Pearson Education, Inc. Quick Review Attractions and interactions between the side chains cause the proteins to fold into precise three-dimensional shapes Protein shape determines its function Proteins are denatured and their shapes changed by Heat Acids Bases Salts Mechanical agitation © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc.  AMINO ACID: STRUCTURE AND CLASSIFICATION. Amino Acids are the building units of proteins. There are about 300 amino acids occur in nature. Only 20 of them enter in proteins synthesis. Structure of amino acids: Four different groups are attached to α- carbon: amino group COOH group Hydrogen atom and side Chain (R). © 2010 Pearson Education, Inc.  Each amino acid, aside from its name, has a three letter abbreviation and a one letter code. © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc.  At physiological pH (7.4), -COOH group is dissociated forming a negatively charged carboxylate ion (COO- ) and amino group is protonated forming positively charged ion (NH3 + ) forming Zwitter ion. © 2010 Pearson Education, Inc.  Proline is an imino acid not amino acid. © 2010 Pearson Education, Inc.  Classification of Amino Acids: I. Classification by R group II. Chemical Classification III. Nutritional Classification IV. Metabolic Classification © 2010 Pearson Education, Inc.  Classification by R group © 2010 Pearson Education, Inc. Polar amino acids: in which R contains polar hydrophilic group so can forms hydrogen bond with H2O. In those amino acids, R may contain: OH group : as in serine, threonine and tyrosine - SH group : as in cysteine amide group: as in glutamine and aspargine NH2 group or nitrogen act as a base (basic amino acids ): as lysine, arginine and histidine COOH group (acidic amino acids): as aspartic and glutamic. Classification according to polarity of side chain (R): © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc.  Non polar amino acids: R is alkyl hydrophobic group which can’t enter in hydrogen bond formation. 9 amino acids are non-polar ( glycine, alanine, valine, leucine, isoleucine, phenyl alanine, tryptophan, proline and methionine). © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc.  The twenty common amino acids are often referred to using three-letter abbreviations. The structures, names, and abbreviations for the twenty common amino acids are shown below. Note that they are all α-amino acids. © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc.  Nutritional Classification 1- Essential Amino Acids 10 in number, Can’t be synthesized in the body, essential to be taken in diet. Their deficiency affects growth, health and protein synthesis. 2- Semi-essential formed in the body but not in sufficient amount for body requirements especially in children. Arginine and histidine are semi-essential. 3- Non-essential can be synthesized in the body. © 2010 Pearson Education, Inc.  Non Standard Amino Acids > 700 non standard amino acids have been detected in living organisms. Many are metabolic intermediates eg. ornithine and citrulline are intermediates in urea biosynthesis Amino Acid Derivatives Chemical derivatives of amino acids also have important biological functions, eg. Catecholamines (below) lack the a-carboxylate of amino acids © 2010 Pearson Education, Inc.  GABA & Dopamine are neurotransmitters. Histamine mediates parts of the immune response. © 2010 Pearson Education, Inc.  Functions of Amino Acids Apart from being the monomeric constituents of proteins and peptides, amino acids serve variety of functions. (a) Some amino acids are converted to carbohydrates and are called as glucogenic amino acids. © 2010 Pearson Education, Inc.  (b) Specific amino acids give rise to specialised products, e.g. Tyrsione forms hormones such as thyroid hormones, (T3, T4), epinephrine and norepinephrine and a pigment called melanin. Tryptophan can synthesise a vitamin called niacin. Glycine, arginine and methionine synthesise creatine. © 2010 Pearson Education, Inc.  Glycine and cysteine help in synthesis of Bile salts. Glutamate, cysteine and glycine synthesis glutathione. Histidine changes to histamine on decarboxylation. Serotonin is formed from tryptophan. Glycine is used for the synthesis of haem.. © 2010 Pearson Education, Inc.  Pyrimidines and purines use several amino acids for their synthesis such as aspartate and glutamine for pyrimidines and glycine, aspartic acid, Glutamine and serine for purine synthesis c) Some amino acids such as glycine and cysteine are used as detoxicants of specific substances. (d) Methionine acts as “active” methionine (S-adenosylmethionine) and transfers methyl group to various substances by transmethylation. (e) Cystine and methionine are sources of sulphur © 2010 Pearson Education, Inc.  Introduction ▪ Proteins are polymers of amino acids that are linked covalently through peptide bonds. ▪ Aminoacid: an organic cmpound containing both amino and carboxyl functional groups; simplest units of proteins ▪ There are 20 different kinds of amino acids, combined in different proportion and arrangements to build all protein molecules ▪ When only two amino acids combine by peptide bond ,it is called dipeptide, when amino acids involved in the bond formation become 3, 4, 5 they are named as tri-, tetra-, and penta- peptides respectively. © 2010 Pearson Education, Inc. Proteins, continued.. ▪ All proteins contain carbon, hydrogen, oxygen, and nitrogen; some proteins may also contain sulfur phosphorous, copper, iron, zinc, iodine, and other elements. ▪ The presence of nitrogen in all proteins sets them apart from carbohydrates and lipids. ▪ The average nitrogen content of proteins is approximately 16%. © 2010 Pearson Education, Inc. Proteins, continued.. ▪ Comprises 50-70% of cell’s dry weight ▪ Found in cells, as well as in all fluids, secretions, and excretions ▪ more than 300 different types of plasma proteins are discovered © 2010 Pearson Education, Inc. Classification Protein classification Proteins may classified based on what they are built from as: simple proteins complex proteins : - apoproteins, - conjugated proteins © 2010 Pearson Education, Inc. Protein classification, continued…. Based on their shape proteins can be classified as fibrous proteins and globular proteins Proteins have four levels of structure -Primary structure -Secondary structure -Tertiary structure -Quaternary structures. © 2010 Pearson Education, Inc.  Function of Proteins used to construct or build our body catalyze biochemical reactions as an enzyme regulate body metabolism as hormones protect our body from foreign body attack as an antibody and components of complement maintain osmotic pressure in plasma Transport different lipids, minerals, hormones, vitamins etc as hemoglobin, apolipoprotein, albumin etc assist to arrest bleeding and maintain homeostasis as coagulation factor © 2010 Pearson Education, Inc. Plasma proteins Many different proteins are present in the blood, and collectively known as plasma proteins. They include Albumin, Alpha1Acid glycoproteins, ceruloplasmin, C-reactive protein, complements, fibrinogen and immunoglobulins. Most of plasma proteins are synthesized and catabolized in the liver. © 2010 Pearson Education, Inc. Clinical significance of protein The two general causes of alteration of serum total protein are: change in volume of plasma water change in concentration of protien The relative hypoproteinemia --hemodilution. The relative hyperproteinemia-hemoconcentration. © 2010 Pearson Education, Inc. Plasma proteins with Clinical significance Albumin the most abundant plasma protein extra vascular body fluids, including CSF, Interstitial fluid, urine, and amniotic fluid. accounts approximately one-half of the plasma protein mass. a globular protein, with molecular mass of 66.3 KD. Because of its high net negative charge at physiological pH, highly soluble in water, but does not have carbohydrate side chain. © 2010 Pearson Education, Inc.  Functions of albumin maintaining the colloidal osmotic pressure in both the vascular and extra vascular space with continuous equilibration in between Binding and transportation of large number of compounds, including free fatty acids, phospholipids, metallic ions, amino acids, drugs, hormones and bilirubin. © 2010 Pearson Education, Inc. Clinical significance Cause for an increase level of albumin acute dehydration and has no clinical significance. © 2010 Pearson Education, Inc. Decreased levels of albumin seen in.. Edema and ascitis Analbuminemia Urinary loss Inflammatory conditions Gastrointestinal loss Hepatic disease Protein energy malnutrition © 2010 Pearson Education, Inc. Alpha 1 –fetoprotein [AFP] one of the first α –globulin appear in mammalian sera during development of the embryo Dominant serum protein in early embryonic life synthesized primarily by the fetal yolk sac and liver.. contains approximately 4% carbohydrate with a molecular mass approximately 70KD. © 2010 Pearson Education, Inc. Clinical significance High AFP levels seen in: open neural tube or abdominal wall defect in fetus. Multiple fetuses, fetal demise, fetomaternal bleeding, and incorrect estimation of gestational age Hepatocellular and germ cell carcinomas in childhood and adults © 2010 Pearson Education, Inc.  C-reactive protein The first APPs to become elevated in inflammatory diseases consists of five identical subunits and is synthesized primarily by liver. C-reactive protein (CRP) found in sera of acutely ill individuals from S. pneumonia CRP activates the classic complement path way starting at C1q and initiates opsonization, phagocytosis, and lysis of invading organisms. such as bacteria and viruses. © 2010 Pearson Education, Inc. CRP continues… CRP can recognize potentially toxic autogenous substances released from damaged tissue, to bind them, and then detoxify or clear them from the blood. © 2010 Pearson Education, Inc. Clinical significance CRP levels usually rise after myocardial infraction, stress, trauma, infection, inflammation, surgery, or neoplastic proliferation. CRP is clinically useful for Screening for organic disease Assessment of the activity of inflammatory diseases © 2010 Pearson Education, Inc.  Detection of inter-current infection in systemic lupus erythematosus (ALE), in leukemia, or after surgery\ management of neonatal septicemia and meningitis Cord blood normally has low CRP concentration, but in intrauterian infection, the concentration will be high. © 2010 Pearson Education, Inc.  properties protein Molecular size Differential solubility Electrical charge Adsorption on finely divided inert materials Specific binding to antibodies, coenzymes, or hormone receptors © 2010 Pearson Education, Inc. Specific methods for total protein determination. Biuret method Direct photometric methods. Dye-binding methods. Turbidimetric and nephelometric methods © 2010 Pearson Education, Inc.  Biuret method Principle of the test peptide bonds react with Cu2+ ions in alkaline solutions to form a colored product absorbance is measured spectrophotometrically at 540nm. © 2010 Pearson Education, Inc.  Biuret, continued…. The biuret reaction occurs with other compounds with structural similarity. One copper ion probably is linked to 6 nearby peptide linkage by coordinate bonds. Amino acids and di peptides do not react, but tri peptides, oligo peptides, and polypeptides react to yield pink to reddish- violet products. The intensity of the color produced is proportional to the amount of protein present in the reaction system. Detect between 1 and 15 mg of protein in the aliquot measured, an amount present in 15 to 200 μl of a serum containing protein at 7gm/dl. © 2010 Pearson Education, Inc.  Biuret, continued.. Specimen type, source of errors, and preservation ▪ Either serum or plasma, but serum is preferred. ▪ A fasting specimen may be required to decrease the risk of lipemia. ▪ Ammonium ions interfere ▪ Hemolysis should be avoided. ▪ Serum samples are stable for atleast 1week at room temperature and for 1 month at 2 to 4o C. ▪ Specimens that have been frozen and thawed should be mixed thoroughly before assay. © 2010 Pearson Education, Inc.  Direct photometric methods. Principle of the test. ▪ Absorption of UV light at 200-225 nm and 272 – 290 nm is used ▪ Absorption of UV light at 280 nm depend on the aromatic rings of tyrosine and tryptophan ▪ Peptide bonds are responsible for UV absorption (70% at A205) ; ▪ Specific absorption by proteins at 200 to 225 nm 10 to 30 times greater than at 280 nm. © 2010 Pearson Education, Inc.  Limitations of the direct photometric methods Accuracy & specificity suffer from ▪ uneven distribution of tyrosine and tryptophan among individual proteins ▪ the presence of free tyrosine and tryptophan, uric acid, and bilirubin, which also absorb light near 280nm. ▪ interferences from free tyrosine and tryptophan is significant at 200 to 225nm. ▪ A 1:1000 or 1:2000 dilution of serum with sodium chloride,0.15 mol/l ,circumvents this interferences. © 2010 Pearson Education, Inc. Dye-binding methods Principle of the test ▪ Based on the ability of proteins to bind dyes such as amido black 10B and Coomassie Brilliant Blue. ▪ The method is simple, easy, and linear up to 150 mg/dl. ▪ assay of total protein in CSF and urine uses CBB G- 250 © 2010 Pearson Education, Inc. Limitation of dye binding methods ▪ unequal affinities and binding capacities of individual proteins for dyes ▪ inability to define a consistent material for use as a calibrator. © 2010 Pearson Education, Inc.  Turbidimetric and nephelometric methods Principle of the test ▪ Protein in the sample is precipitated with addition of sulfosalicylic acid alone, with sulfosalicylic acid in combination with sodium sulfate or trichloroacetic acid (TCA), or with TCA alone to produce turbidity. ▪ Degree of turbidity measured with Turbidometeric or nephelometric methods © 2010 Pearson Education, Inc. Assay Techniques for serum albumin ▪ Dye-binding methods ▪ Salt fractionation or the 'salting-out' procedure ▪ By difference ▪ Electrophoresis ▪ Immunochemical techniques. © 2010 Pearson Education, Inc. Dye binding method BCG Method ▪ Test principle: Albumin and BCG are allowed to bind at pH 4.2, in succinate buffer, ▪ absorption of the BCG-albumin complex is measured at 628 nm. ▪ At pH 4.2, albumin acts as a cation to bind the anionic dye. ▪ The reaction is extremely fast and goes to completion in only a few seconds. © 2010 Pearson Education, Inc. Reference Range Adult serum albumin ▪ Recumbent: 3.5 - 5.0 g/dl ▪ In the upright position levels are about 0.3 g/dl higher because of hemoconcentration. © 2010 Pearson Education, Inc. Source of error and remedy ▪ hyperlipemia ▪ hyperbilirubinemia ▪ hemolysis ▪ can generally be eliminated (minimized) by dilution of serum 1:250 © 2010 Pearson Education, Inc. BCP Method Test principle: ▪ Yellow BCP dye, buffered at pH 5.2 with acetate ▪ turns green when complexed with albumin. ▪ Absorbance of the green complex is measured at 603 nm. © 2010 Pearson Education, Inc. Specimen ▪ serum is recommended ▪ Results tend to be erroneous if the overall serum protein pattern is abnormal © 2010 Pearson Education, Inc. Methods for the determination of total globulins Methods for the quantitative determination of total globulins ▪ Colorimetric method ▪ Globulin by difference ▪ Electrophoresis ▪ Immunochemical technique © 2010 Pearson Education, Inc. Colorimetric method Test principle: ▪ glyoxylic acid reacts with tryptophan residues of proteins to form a purple color. ▪ Copper sulphate is added to enhance color formation. ▪ human globulins are known to contain 2 - 3% tryptophan © 2010 Pearson Education, Inc.  Serum Protein Electrophoresis Electrophoresis is widely used in clinical laboratories to study and measure the protein content of biological fluids- serum, urine or csf. Screening tool for prtein abnormalities Electrophoresis techniques include: Cellulose acetate electrophoresis Gel and capillary electrophoresis Specialized techniques termed western blotting, immunofixation, and two-dimensional electrophoresis © 2010 Pearson Education, Inc. Methodology for Protein Electrophoresis ▪ Patient’s specimen is placed into a sample trough within agarose gel, is placed in an alkaline buffer solution ▪ a standardized voltage is applied and allowed to run for 1hr ▪ the agarose gel is processed in acetic acid and alcohol washes to fix the proteins in the agarose. ▪ the protein fractions are stained with Coomassie Brilliant Blue protein stain. © 2010 Pearson Education, Inc.  ▪ After a second wash, fixed protein bands can be visualized and quantified with densitometry. ▪ In normal serum electrophoresis 5-6 bands are visible: ▪ Albumin ▪ Globulins: α1-, α2-, β-, and γ- © 2010 Pearson Education, Inc. Materials and procedures of protein electrophoresis ▪ Buffer: barbital with an ionic strength of 0.05 and pH 8.6 ▪ Sample volume: 3 to 5 µl ▪ Power supply: 1.5 mA per 2-cm width of cellulose acetate medium; 10mA per 1-cm width of agarose medium ▪ Run time:40 to 60 min producing a 5- to 6-cm migration distance for aalbumin © 2010 Pearson Education, Inc.  Normal serum protein electrophoresis pattern Albumin 1 2   + - © 2010 Pearson Education, Inc. Specimen for electrophoresis Serum CSF Concentrated urine © 2010 Pearson Education, Inc. Interpretation of Results ▪ Reference Range of total protein Serum---------------------------6-8 g/dl CSF----------------------------- 8-32 mg/dl ▪ For electrophoresis -serum: albumin-----------------3.9-5.1 g/dl α1-globulin------------0.2-0.4 g/dl α2-globulin------------0.4-0.8 g/dl β-globulin--------------0.5-1.0 g/dl γ-globulin---------------0.6-1.3 g/d ▪ Compare the patient results with the reference range to assess for hyper- or hypoglycemia © 2010 Pearson Education, Inc. Quality Control ▪ A normal & abnormal quality control sample should be analyzed along with patient samples, using Westgard or other quality control rules for acceptance or rejection of the analytical run. Assayed known samples Commercially manufactured ▪ Validate patient results ▪ Detects analytical errors. © 2010 Pearson Education, Inc.  Documentation of protein Results Record patient results in result logbook Record QC results in QC logbook Retain records for recommended time © 2010 Pearson Education, Inc.  summary ▪ Proteins are polymers of amino acids that are linked covalently through peptide bonds. ▪ The presence of nitrogen in all proteins sets them apart from carbohydrates and lipids. ▪ Proteins are classified based on the number of amino acid molecules ,composition of amino acids. ▪ Protein have four structural levels;10,20,30,and 40. ▪ Properties of proteins include molecular size, differential solubility, electrical charge, adsorption on finely divided inert materials, and specific binding to antibodies, coenzymes, or hormone receptors © 2010 Pearson Education, Inc.  Summary, continued… ▪ Proteins function includes building our body , serving as enzymes, as antibody. etc..’ ▪ Major plasma proteins include Albumin, Alpha1Acid glycoproteins, ceruloplasmin, C-reactive protein, complements, fibrinogen and immunoglobulins ▪ Increase level of protein caused by acute dehydration and has no clinical significance; decreased levels of proteins seen in edema and ascitis, analbuminemia, urinary loss, inflammatory conditions, gastrointestinal loss, hepatic disease, protein energy malnutrition. ▪ Specific methods for total protein determination include Biuret method, direct photometric methods, dye-binding methods, turbidimetric and nephelometric methods ▪ Serum protein electrophoresis used to fractionate proteins © 2010 Pearson Education, Inc.  Amino acids Of the 20 amino acids that exist, 9 are essential amino acids, and 11 are non- essential © 2010 Pearson Education, Inc. AMINO ACID: Sequence  Dipeptide – 2 amino acids  Tripeptide – 3 amino acids  Oligopeptides – 4-10 amino acids  Polypeptide – more than 10 amino acids  Proteins in the body and diet are long polypeptides (100s of amino acids) © 2010 Pearson Education, Inc. AMINO ACID: Sequence  Dipeptide – 2 amino acids  Tripeptide – 3 amino acids  Oligopeptides – 4-10 amino acids  Polypeptide – more than 10 amino acids  Proteins in the body and diet are long polypeptides (100s of amino acids) © 2010 Pearson Education, Inc.  AMINO ACIDS: Structure Consist of a central carbon atom bonded to: a hydrogen, a carboxylic acid, an amino group, and an additional side group that is unique to each amino acid © 2010 Pearson Education, Inc.  Digestion of proteins © 2010 Pearson Education, Inc.  Initial digestion of protein in stomach  No digestion of protein takes place in the mouth,  Hydrochloric acid denatures protein and also converts pepsinogen to pepsin  Pepsin breaks the protein down into peptides of various lengths and some amino acids  Pepsin act only at pH 1.6-3.2  Pepsin completes ~ 10-20% of digestion © 2010 Pearson Education, Inc. Denaturing of Proteins Acid, alkaline, heat and alcohol, can disrupt the chemical forces that stabilize proteins and can cause them to lose their shape (denature) Denaturing of proteins happens during food preparation (cooking, whipping, adding acids) or digestion (in the stomach with hydrochloric acid) © 2010 Pearson Education, Inc.  Action of Proteolytic enzymes  Pepsin hydrolyses the bonds between aromatic amino acids(phenylanine or tyrosine) and a second amino acid  So the product of pepsin hydrolysis is polypeptides of diverse sizes © 2010 Pearson Education, Inc.  Polypeptidases Trypsinogen and chymotrypsinogen (proenzymes) are secreted by pancreas in response to protein in the small intestine They will be activated to trypsin and chymotrypsin (now called proteases) © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc.  Peptidases hydrolyse proteins  These enzymes can either cleave internal peptide bonds (i.e. endopeptidases)  exopeptidases cleave off one amino acid at a time from either the –COOH or –NH2 terminal of the polypeptide (i.e. they are carboxypeptidases , and aminopeptidases, respectively) © 2010 Pearson Education, Inc.  The endopeptidases cleave the large polypeptides to smaller oligopeptides, which can be acted upon by the exopeptidases to produce the final products of protein digestion, amino acids, di- and tripeptides, which are then absorbed by the enterocytes © 2010 Pearson Education, Inc. Further hydrolysis by Peptidases By the action of endo and exopeptidases some free amino acids are liberated in the intestinal lumen, But others are liberated at the cell surface by the aminopeptidases, carboxypeptidases, endopeptidases, and dipeptidases in the brush border of the mucosal cells. © 2010 Pearson Education, Inc.  Absorption of proteins © 2010 Pearson Education, Inc.  Transport of amino acids and polypeptides in thedi-enterocytes  The and tripeptides are actively transported into enterocytes by a system known as peptide transporter 1) that requires H + instead of Na + © 2010 Pearson Education, Inc.  At basolateral membrane The movement of any one amino acid can occur through one or more amino acid transporters. At least five amino acid transporters are present in the basolateral membrane. Three amino acid transport processes on the basolateral membrane mediate amino acid exit from the cell into the blood Two other amino acid transporters mediate uptake from the blood for the purposes of cell nutrition. © 2010 Pearson Education, Inc.  Amino acid transport at basolateral Individual amino acids are transported across the basolateral membrane without the need for cotransport. Many different amino acid transporters are located on the basolateral membrane and provide specificity © 2010 Pearson Education, Inc.  Diseases associated with absorption of proteins Hartnup disease and cystinuria are hereditary disorders of amino acid transport across the apical membrane. These autosomal recessive disorders are associated with both small intestine and renal tubule abnormalities the absorption of neutral amino acids in the case of Hartnup disease and of cationic (i.e., basic) amino acids and cystine in the case of cystinuria. © 2010 Pearson Education, Inc. References Lippincott’s Illustrated Reviews: Physiology (2013) Medical Physiology, Updated second edition (walter F. Boron, MD, phd) Berne & levy, physiology, sixth edition, updated edition Ganong’s Review of Medical Physiology, 26 t h e d i t i o n © 2010 Pearson Education, Inc.