AMINO ACID METABOLISM AND RELATED DISORDERS.pptx

AMINO ACID METABOLISM AND RELATED DISORDERS D. A BERKOH DEPT. OF MEDICAL LABORATORY SCIENCE UENR-SUNYANI  HELLO! “We are the basis of structure and function of life, composed of twenty amino acids, th...

AMINO ACID METABOLISM AND RELATED DISORDERS D. A BERKOH DEPT. OF MEDICAL LABORATORY SCIENCE UENR-SUNYANI  HELLO! “We are the basis of structure and function of life, composed of twenty amino acids, the building blocks; organized into primary, secondary, tertiary and quaternary structure; classified as simple, conjugated and derived proteins…” 2 08/28/2024 D.A Berkoh  PROTEINS The most abundant organic molecules of the living system They are found in every part of the cell and make up 50% of cellular dry weight They form the fundamental basis of structure and function of life. 3 08/28/2024 D.A Berkoh  ORIGIN OF THE WORD “PROTEIN” Derived from the Greek word “Proteios”; which means “holding first place” A Swedish chemist by name Berzelius first suggested the name “proteins” to the organic compounds of utmost importance to life In 1838, a Dutch chemist; Mulder, used the term proteins for the high molecular weight nitrogen-rich and most abundant substances present in plants and animals. 4 08/28/2024 D.A Berkoh Functions of Proteins Storage Muscle Genetic control proteins contraction Enzymes , Hormones respiration dynamic Clotting factors Proteins immunoglobul ins Strength and Structural/ structural static support 5 08/28/2024 D.A Berkoh  Proteins that perform these dynamic functions are referred to as “working horses” of the cell. Proteins are made up of 5 major elements: 1. Carbon - 50-55% 2. Hydrogen - 6 to 7.3% 3. Oxygen – 19-24% 4. Nitrogen – 13-19% 5. Sulphur – 0-4% Proteins may also contain other elements such as P, Fe, Cu, Mg, Mn, Zn, etc. 6 08/28/2024 D.A Berkoh  Nitrogen is an essential component of proteins which constitutes averagely 16% of the protein’s structure. In the lab the concentration or amount of Nitrogen is estimated using the Kjeldahl’s method to find out the amount of protein present in food and biological fluids (blood and/or urine). Proteins are polymers of amino acids; which on hydrolysis with concentrated HCl for several hours yield L-α-amino acids. 7 08/28/2024 D.A Berkoh  Let’s talk about Amino Acids….. 8 08/28/2024 D.A Berkoh  Amino acid Structure  Amino acids are building blocks of proteins - Have properties that enable them carry out various biological functions such as: (i) ability to form polymers(polymerize) (ii) possess acid-base properties (iii) varied physical properties (iv) varied chemical functionality 9 08/28/2024 D.A Berkoh  Made up of a carboxyl group (except proline), an amino group, and a side chain Amino acids share many features but differ at their side chains(R groups) The amino group is basic; while the carboxyl group is 10 08/28/2024 D.A Berkoh  At physiological pH (7.2-7.4), the amino group on the amino acid structure bears a positive charge/protonized (NH3+) while the carboxylic acid group bears a negative charge (COO-) The R group determines the identity of the amino acid. Eg: if the R group is a H, the amino acid is Glycine. If it’s a methyl group (CH 3), then it is Alanine. The properties of the R group also determines the amino acid’s chemical behavior ie acidic, basic, polar or nonpolar, etc. Some amino acids have R groups with special properties that are important for protein structure. 11 08/28/2024 D.A Berkoh  By The Way….. 12 08/28/2024 D.A Berkoh Biological Importance of Amino Acids Muscle protein maintenance Potentiation of immune function Affecting neuronal activities in the brain Tissue repair acceleration after burn/trauma Protection of the liver from toxic agents Reducing blood ammonia Imparting pain relief effects  Biological Importance of Amino Acids Lowering blood pressure Modulating cholesterol metabolism Stimulating insulin and growth hormone (GH) secretion.  Metabolism of Amino acids Transfer of an amino group from Transaminati an amino acid to a keto acid Transaminases catalyze this on reaction Removal of an amino group from Deaminati amino acids Ammonia is liberated for urea on synthesis 15 08/28/2024 D.A Berkoh  Carbon skeleton of the amino acids is first converted to keto acids by transamination The keto acids formed meet one of the following fates: Used to generate energy Used to synthesize glucose Used for the formation of fats or ketone bodies Used for the production of non-essential amino acids 16 08/28/2024 D.A Berkoh  Salient Features of Transamination The enzymes (transaminases) require pyridoxal phosphate ( a coenzyme derived from vitamin B6) Each pair of amino acids and ketoacids have specific transaminases but only AST and ALT make significant contributions for transamination reactions No free ammonia is liberated, only the transfer of amino groups occurs Transamination reactions are reversible 17 08/28/2024 D.A Berkoh 18 08/28/2024 D.A Berkoh  Transamination reactions are important for the redistribution of amino groups and production of non-essential amino acids as per required by the cell. It involves both catabolism and anabolism of amino acids Excess amino acids are diverted towards energy generation Amino acids undergo transamination to finally concentrate nitrogen in glutamate; which is the only amino acid that undergoes oxidative deamination to release free ammonia for the synthesis of urea All amino acids, except lysine, threonine, proline and hydroxyproline participate in transamination reactions 19 08/28/2024 D.A Berkoh  Transamination is not restricted to alpha amino groups only. δ-amino group of ornithine for instance is also transaminated. Transaminases in serum are used for diagnostic and prognostic purposes Process occurs in two stages: Transfer of an amino grp to the coenzyme pyridoxal phosphate (derived from Vit B6) to form pyridoxamine phosphate An amino grp from pyridoxamine phosphate is then transferred to a keto acid to produce a new amino acid and the enzyme with pyridoxal phosphate (PLP) is regenerated. All transaminases require PLP*** 20 08/28/2024 D.A Berkoh  Salient Features of Deamination Results in the liberation of ammonia for the synthesis of urea Carbon skeletons of amino acids are converted to keto acids. Deamination may be oxidative or non-oxidative Transamination and deamination occur simultaneously with glutamate as the central molecule 21 08/28/2024 D.A Berkoh  Oxidative deamination This is the liberation of free ammonia from the amino group of amino acids coupled with oxidation Takes place mostly in the liver and kidney Purpose of this reaction is to provide NH 3 in order to make urea and α-keto acids for a variety of reactions including energy generation 22 08/28/2024 D.A Berkoh  Non-oxidative deamination Liberation of ammonia in the absence of oxygen Hydroxy amino acids: Serine, Threonine and Homoserine undergo non- oxidative deamination catalysed by pyridoxal phosphate-dependent dehydrases Sulphur amino acids: cysteine and homocysteine undergo deamination coupled with desulfhydration to give keto acids Histidine is acted on by histidase to liberate ammonia by a non-oxidative deamination process 23 08/28/2024 D.A Berkoh  1 2 3 24 08/28/2024 D.A Berkoh  Overview of Amino acid Metabolism 25 08/28/2024 D.A Berkoh  Metabolism of Ammonia Formed from amino acids (transamination and deamination reactions), biogenic amines, amino group of purines and pyrimidines and by the action of intestinal bacteria (urease) on urea Transported between various tissues and the liver in the form of glutamine or alanine Alanine is important for transporting NH 3 from muscle to liver by the glucose-alanine cycle Glutamine is the storehouse of NH3 where it serves as a storage and transport form. Synthesized in the liver, brain and muscle 26 08/28/2024 D.A Berkoh  Functions of Ammonia Involved in the synthesis of : Non-essential amino acids Purines Pyrimidines Amino sugars Asparagine Ammonium ions (NH4+) help to maintain acid-base balance 27 08/28/2024 D.A Berkoh  Disposal and Toxicity of Ammonia Mammals (including humans) convert ammonia to urea which is non-toxic and easily excreted A slight or marginal elevation of ammonia in blood is harmful to the brain Accumulation can cause slurred speech, blurred vision and tremors May cause coma and death if not checked 28 08/28/2024 D.A Berkoh  Hyperammonaemia Elevation of blood NH3. May be genetic or acquired Impaired urea synthesis due to defect in any of the enzymes of the urea cycle lead to hyperammonaemia This can cause hepatic coma and mental retardation Acquired hyperammonaemia may be due to hepatitis, alcoholism, etc where synthesis of urea is defective leading to accumulation of ammonia 29 08/28/2024 D.A Berkoh Ammonia toxicity Explanation Accumulation of NH3 shifts equilibrium to the right, increasing levels of glutamate and depleting α-ketoglutarate α-ketoglutarate is a key intermediate in the TCA cycle. Its depletion impairs the TCA cycle, reducing the net production of ATP by the brain Ammonia toxicity therefore interferes with the brain’s production 30 08/28/2024 D.A Berkoh  Reversing Ammonia toxicity Administration of IV Sodium benzoate and phenyllactate These compounds condense with glycine and glutamate respectively to form water soluble products that can be easily excreted By this way ammonia is trapped and removed from the body Sometimes haemodialysis is also done to reverse ammonia toxicity 31 08/28/2024 D.A Berkoh  Urea End product of protein metabolism (or amino acid metabolism) Synthesized in the liver and transported to the kidneys for excretion through urine. Small amount enters the intestine where it is broken down to CO 2 and NH3 by the bacterial enzyme urease Ammonia formed is either lost in faeces or absorbed into blood In renal failure, urea is elevated in the blood resulting in increased formation of NH3 (hyperammonaemia). Treatment is by giving oral antibiotics (Neomycin) to kill intestinal bacteria 32 08/28/2024 D.A Berkoh Clinical Importance of Blood Urea Blood urea in normal, healthy individuals is between 10-40 mg/dl High protein diet increases urea level but within normal range 15-30 g of urea excreted in urine per day Blood urea [ ] used to screen for renal function Blood urea elevation classified into 3 main categories: Pre-renal Renal and Post-renal 33 08/28/2024 D.A Berkoh 1. Pre-renal: associated with increased protein breakdown, leading to negative nitrogen balance. Negative nitrogen balance observed in major surgeries, prolonged fever, diabetic coma, thyrotoxicosis, bleeding disorders and leukaemia. 2. Renal: in renal disorders like acute glomerulonephritis, chronic nephritis, nephrosclerosis, polycystic kidney disease, blood urea is increased 3. Post-renal: whenever the urinary tract is blocked (obstructed) by for eg tumours, stones, an enlarged prostate gland, etc, blood urea is elevated. This is due to increased reabsorption of urea from the renal tubules 34 08/28/2024 D.A Berkoh  Non-protein Nitrogen (NPN) Refers to all substances that contain nitrogen other than proteins These include urea, creatinine, uric acid, peptides, amino acids NPN in healthy individuals is 20-40 mg/dl BUN = ½ NPN NPN = 2BUN BUN or NPN sometimes employed for the assessment of kidney function 35 08/28/2024 D.A Berkoh 36 08/28/2024 D.A Berkoh  Glycine (Gly, G) One of the commonest amino acids found in protein (collagen contains abt 30% glycine) Made from serine by the enzyme serine hydroxymethyl transferase which is dependent on tetrahydrofolate (THF) Can also be obtained from threonine, catalyzed by threonine aldolase Undergoes oxidative deamination by glycine synthase to liberate NH 4+, CO2 and N5, N10-methylene THF to provide a route for glycine breakdown in mammals 37 08/28/2024 D.A Berkoh  Specialized products of Glycine Glycine is utilized in the formation of the purine ring (positions 4 & 5 of C and position 7 of N Synthesis of glutathione (γ-glutamyl-cysteinyl-glycine) Functions as a conjugating agent: - conjugation of bile acids (cholic acid and chenodeoxy acid) - detoxification of benzoic acid (commonly used as a food preservative) to hippuric acid 38 08/28/2024 D.A Berkoh  Syhthesis of haem: Glycine condenses with succinyl CoA to form δ-amino levulinate which is a precursor for haem synthesis Biosynthesis of creatine which is reversibly phosphorylated to phosphocreatine and stored in muscle. Creatinine is the anhydride form of creatine which is used to assess kidney function Serum creatinine is considered a more reliable marker of renal function because its concentration is not affected by exogenous or endogenous factors 39 08/28/2024 D.A Berkoh Metabolic Disorders of Glycine 1.Glycinuria rare disorder where serum glycine concentration is normal but very high amounts are excreted in urine. Believed to be caused by defective renal reabsorption Characterized by increased tendency for the formation of oxalate renal stones even with normal urinary oxalate levels 40 08/28/2024 D.A Berkoh 2. Primary hyperoxaluria Due to defect in glycine transaminase coupled with impairment in oxidation of glyoxalate to fumarate Mainly due to defect in protein targeting (transport of protein from one compartment to another). As a result, glycine transaminase is found in mitochondria instead of the peroxisomes. Characterized by increased urinary oxalate resulting in oxalate stones Deposits of oxalate (oxalosis) in various tissues occurs Urinary oxalate is endogenous and not due to dietary consumption of 41 08/28/2024 D.A Berkoh Phenylalanine (Phe, F) and Tyrosine (Tyr, Y) These are aromatic amino acids Phe is an essential amino acid while Tyr is non-essential. Phe is converted to Tyr which is incorporated into proteins and is involved in the synthesis of biologically important compounds such as Epinephrine, norepinephrine, dopamine(catecholamine), thyroid hormones and melanin During degradation, F and Y serve as precursors for the synthesis of glucose and fat (ketogenic and glucogenic amino acids) 42 08/28/2024 D.A Berkoh Disorders of Tyrosine (Phenylalanine) Metabolism 1. Phenylketonuria (PKU) Most common metabolic disorder in amino acid metabolism Occurs due to a deficiency in the enzyme phenylalanine hydroxylase caused by an autosomal recessive gene Net result is that Phenylalanine is not converted to tyrosine PKU causes the accumulation of phenylalanine in tissues and blood and results in increased excretion in urine (as phenylpyruvate, phenyllactate, phenylacetate (gives urine a mousey odour) and phenylglutamine) 43 08/28/2024 D.A Berkoh Clinical Manifestations of PKU Mental retardation Failure to walk or talk Failure of growth, seizures, tremors Patients usually show low IQ if untreated (IQ below 50) Impaired melanin formation (hypopigmentation that causes light skin colour, fair hair, blue eyes, etc) 44 08/28/2024 D.A Berkoh Diagnosis of PKU Diagnosis is done by screening new borns for increased plasma levels of phenylalanine (PKU, 20-65 mg/dl; normal 1-2mg/dl) The test is referred to as the Guthrie test which is a bacterial (Bacillus subtilis) bioassay for phenylalanine It is performed after the baby is fed with breast milk for a couple of days In urine, phenylpyruvate can be detected by the Ferric chloride test where a green colour indicates the presence of phenylketonuria Cultured amniotic cells can also be used in the diagnosis of PKU 45 08/28/2024 D.A Berkoh Treatment of PKU Eating foods that have low phenylalanine content or feeding patients with synthetic amino acid preparations low in phenylalanine Administration of 5-hydroxytryptophan and dopa to restore synthesis of serotonin and catecholamines (in severely affected patients) Early diagnosis and treatment for 4-5 years can prevent brain damage. However restriction to protein diet should continue for many more years in life In PKU, tyrosine cannot be synthesized, hence should be provided in the diet 46 08/28/2024 D.A Berkoh Tyrosinaemia (Tyrosinemia) type I Also known as Richner-Hanhart Syndrome Caused by a defect in the enzyme tyrosine transaminase This results in a blockage of the tyrosine degradation pathway; leading to accumulation and excretion of tyrosine and its metabolites (p- hydroxyphenylpyruvate, p-hydroxyphenyllactate, phydroxyphenylacetate, N- acetyltyrosine and tyramine) Eye lesions and dermatitis are observed in affected individuals and sometimes, though rare, mental retardation where there is disturbance of self-coordination 47 08/28/2024 D.A Berkoh 48 08/28/2024 D.A Berkoh Neonatal Tyrosinemia & Black urine Disease (Alkaptonuria) The enzyme p-hydroxyphenylpyruvate dioxygenase is absent in neonatal tyrosinemia Mostly a temporal condition and usually responds to treatment with ascorbic acid In black urine disease, the enzyme homogentisate oxidase in tyrosine metabolism is defective Homogentisate accumulates in tissues and blood which is excreted in urine. Urine of affected individual on standing is oxidized to quinones which polymerize to give a black or brown colour (almost like coca-cola) Treatment is by consuming diets low in phenylalanine 49 08/28/2024 D.A Berkoh 50 08/28/2024 D.A Berkoh Tyrosinosis or Tyrosemia type II Deficiency in the enzymes fumarylacetoacetate hydroxylase and/or maleylactoacetate isomerase Rare but serious disorder that causes liver failure, rickets, renal tubular dysfunction and polyneuropathy Tyrosine and many of its metabolites are excreted in urine Infants with acute tyrosinosis exhibit diarrhoea, vomiting and “cabbage-like” odour Death may occur due to liver failure within a year and diets low in Methionine, phenylalanine and tyrosine are recommended for treatment 51 08/28/2024 D.A Berkoh 52 08/28/2024 D.A Berkoh Albinism Due lack of melanin synthesis which may be caused by: - deficiency or lack of tyrosinase - decrease in melanosomes or melanocytes - impairment in melanin polymerization - lack of protein matrix in melanosomes - limited tyrosine availability (as substrate) - presence of tyrosinase inhibitors 53 08/28/2024 D.A Berkoh  Albinism mostly caused by a defect in tyrosinase (the enzyme responsible for the synthesis of melanin) Albinos lack melanin and hence makes them sensitive to sunlight. This increases risk of developing skin cancer Photophobia (intolerance to light) is associated with lack of pigment in the eyes 54 08/28/2024 D.A Berkoh 55 08/28/2024 D.A Berkoh Hypopigmentation Reduced synthesis of melanin. There are various types: Vitiligo: is an acquired progressive disease with loss of pigmentation around mouth, nose, eyes and nipples Leukoderma: lack of pigmentation that begins with the hands and then spreads Greying of hair is due to lack of melanin as a result of disappearance of melanocytes from the hair roots 56 08/28/2024 D.A Berkoh  Vitilig o 57 08/28/2024 D.A Berkoh  leukoderm 58 08/28/2024 D.A Berkoh Tryptophan (TRP, W) Both a ketogenic and glucogenic in nature Precursor for the synthesis of NAD+ and NADP+ (coenzymes of niacin), serotonin and melatonin Serotonin (5-hydroxytryptamine) is a neurotransmitter with various functions. It is synthesized in intestinal cells Melatonin is a hormone synthesized in the pineal gland which also has a variety of functions 59 08/28/2024 D.A Berkoh Functions of Serotonin Serotonin is a vasoconstrictor which causes smooth muscle contraction in bronchioles and arterioles Regulates cerebral activity (excitation) Controls sleep, blood pressure and body temperature Initiates release of peptide hormones from the GIT Necessary for peristalsis in the GIT Brain activity stimulant. Deficiency causes depression and in psychosis patients, serotonin levels are low. 60 08/28/2024 D.A Berkoh Functions of Melatonin Involved in circadian rhythms or diurnal variations of the body. Plays a significant role in sleep and wake process Inhibits the production of melanocyte stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH) Has some inhibitory effect n ovarian functions Performs a neurotransmitter function as well 61 08/28/2024 D.A Berkoh  Disorders of Tryptophan Metabolism Hartnup’s Disease Hereditary disorder of tryptophan metabolism Symptoms include dermatitis, ataxia (impaired coordination), mental retardation, etc Characterized by low plasma levels of tryptophan and other neutral amino acids which are elevated in urine Pellagra-like symptoms common in affected patients 62 08/28/2024 D.A Berkoh 63 08/28/2024 D.A Berkoh Sulphur Containing Amino Acids Sulphur containing amino acids are Methionine (essential), Cysteine and Cystine. Cystine and Cysteine are synthesized from Methionine Homocysteine is an intermediate in cysteine synthesis. Elevated levels implicated in coronary artery diseases, aggregation of LDL particles leading to atherogenesis and consequently heart complications In pregnancy, hyperhomocysteinaemia increases risk of neural tube defects in foetus 64 08/28/2024 D.A Berkoh Inborn errors of Sulphur amino acid Metabolism Cystinuria (Cystine-Lysinuria) Characterized by increased excretion of cystine (25-40 times normal) There’s elevated output of Lysine, Arginine and Ornithine in the urine Increased concentration of cystine leads to precipitation and formation of cystine stones in kidney and the urinary tract Treatment is by restricting the intake of dietary cystine and high intake of fluids 65 08/28/2024 D.A Berkoh  Cystinosis (Cystine Storage Disease) caused by defect in lysosomal function Deposition of cystine crystals in many tissues and organs or reticuloendothelial system throughout the body. These include the spleen, lymph nodes, liver, kidney, bone marrow Characterized by impaired renal function, amino aciduria and death of affected individual within 10 years 66 08/28/2024 D.A Berkoh  Homocystinuria type I Accumulation of homocysteine results in thrombosis, osteoporosis and mental retardation There’s deficiency of cystathionine which causes damage to endothelial cells, leading to atherosclerosis Treatment involves consumption of diets low in methionine and high in cystine Two forms of homocystinuria exist: one that can be treated with Vit B 6 supplementation and one that does not respond to the vitamin Patients of homocystinuria usually die of MI, stroke or pulmonary embolism due to high levels of homocysteine 67 08/28/2024 D.A Berkoh 68 08/28/2024 D.A Berkoh Branched Chain Amino acids Valine, Leucine and Isoleucine are essential branched chain amino acids. They are either glycogenic or ketogenic as follows: Valine – glycogenic Leucine – ketogenic Isoleucine – glycogenic and ketogenic 69 08/28/2024 D.A Berkoh Metabolic Defects of Branched chain amino acids Maple Syrup Urine Disease (MSUD) urine of affected individuals smell like maple syrup or burnt sugar Symptoms and complications include: - Accumulation of branched chain amino acids which impair the transport and function of other amino acids - Biosynthesis of protein is reduced - Glutamate dehydrogenase is competitively inhibited - Results in acidosis, lethargy, convulsions, mental retardation, coma and death within a year after birth. 70 08/28/2024 D.A Berkoh 71 08/28/2024 D.A Berkoh  Intermittent Branched Chain Ketonuria Enzyme defect is alpha-keto acid dehydrogenase, same as MSUD The conversion of alpha-keto acid to acyl CoA thioesters is impaired Careful diet planning helps to overcome this disorder Isovaleric acidaemia This is a metabolic disorder specific to leucine where large amounts of isovalerate are excreted into urine. Symptoms include acidosis and mild mental retardation Affected individuals have a “cheesy” odour in their breath and body fluids 72 08/28/2024 D.A Berkoh Other Amino acid metabolism Disorders Histidinemia Due to a defect in the enzyme histidase Characterized by elevated plasma histidine levels and increased excretion of imidazole pyruvate and histidine in urine Patients are mentally retarded and have speech defects No treatment is able to improve this condition 73 08/28/2024 D.A Berkoh Hyperprolinemia type I The enzyme proline oxidase is defective Type II associated with hydroxyproline metabolism Hyperargininemia Defect in the enzyme arginase 74 08/28/2024 D.A Berkoh 75 08/28/2024 D.A Berkoh 76 08/28/2024 D.A Berkoh 77 08/28/2024 D.A Berkoh 78 08/28/2024 D.A Berkoh Thank you!!! 79 08/28/2024 D.A Berkoh