Glycine Amino Acid Metabolism - Ch3 Lecture 3 PDF

Glycine amino acid metabolism Nature: Neutral aliphatic amino acid. It is glucogenic amino acid. It is non-essential amino acid. Synthesis: 1. Threonine. 2. Serine. 3. Glyoxylic acid by transaminase. 4. Denovo synthesis from ammonia & CO2 by glycinesynthase. 5. From choline through c...

Glycine amino acid metabolism Nature: Neutral aliphatic amino acid. It is glucogenic amino acid. It is non-essential amino acid. Synthesis: 1. Threonine. 2. Serine. 3. Glyoxylic acid by transaminase. 4. Denovo synthesis from ammonia & CO2 by glycinesynthase. 5. From choline through choline cycle.  Catabolic fates: 1. Production of CO2 + NH3 by glycine cleavage enzyme. 2. Glyoxylic acid by oxidative deamination or transamination. It undergoes oxidative decarboxylation to form formic acid"formate“ or transaminated into glycine. 3 Pyruvate, (serine hydroxymethyl transferaseand dehydratase) so it is a gluconeogenic amino acid as pyruvate can be converted then into glucose via gluconeogenesis. 4 Detoxification reactions by conjugation: Thisoccur in liver to detoxify several drugs & benzoic acid (which used to preserve food).Benzoic acid converted into non-toxic compoundcalled Hippuric acid. Anabolic fates: 1. Protein synthesis: e.g. Collagen. 2. Purine synthesis. 3. Porphyrins synthesis: which is the precursor of hemoglobin. 4. Bile salts synthesis. 5. Glutathione synthesis: It presents in two forms: A. Reduced form "G-SH": which contains free SH " sulfhydyrylgroup". B. Oxidized form "G-S-S-G": This contains a disulfide bond With no free SH group. Functions of glutathione: 1. Amino acid absorption. 2. Coenzyme for several enzymes. 3. Detoxification reactions by conjugation in liver. 4. Hydrogen donor in oxidation-reduction reactions. 5. Inactivates insulin by breakdown its disulfide bond. 6. Protect cell membrane from damage e.g. prevent Hemolysis of R.B.Cs & protect β-cell of pancreas from oxidizing agents.  6. Creatine synthesis Creatine presents in both blood & muscles. In blood, it presents only in free form "creatine". In muscles: It presents in both free form & creatine phosphate "Creatine-P or phosphagen". – During rest: creatine is phosphorylated by creatine phosphokinase "CPK" using ATP as phosphate donor & form creatine phosphate "stored energy". – During muscular exercise : creatine phosphate is dephosphorylated to regenerate ATP to be used as source of energy , catalyzed by creatine- ATPtransphosphorylase as follow:  Creatine synthesized from arginine and glycine amino acids by two reactions; the first reaction is transamidation in the kidney, and the second reaction is transmethylation in the liver. 1-2% daily of total body creatine or creatine-P is dehydrated or dephosphorylated & dehydrated to form creatinine which is the end product of creatine metabolism & diffuse rapidly to blood to be excreted by the kidneys in urine. Serum creatinine= 0.6-1.2 mg/dl. Diagnostic importance of determination of serumcreatinine: 1. Creatinine clearance rate from blood to the urine is a kidney function test. 2. High blood creatinine & urea are indicators ofrenal impairment e.g. renal failure.