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Conversion of Amino Acids to Specialized Products Amino acids • In addition to their roles in proteins and polypeptides, • amino acids participate in a wide variety of additional biosynthetic processes. Glycine • Glycine conjugates – Glycocholic acid – Hippuric acid – Urinary metabolites of many drugs • Incorporated into – Creatine – Heme – Purines Sources of the nitrogen and carbon atoms of the purine ring Biosynthesis of hippurate Serine • Biosynthesis of – Phospholipid – Sphingosine • Purines – Carbons 2 & 8 • Methyl group of thymine β-Alanine • • • • Metabolite of cysteine Coenzyme A Carnosine From – Cytosine – Carnosine – Anserine β-Alanyl Dipeptides • Carnosine & anserine – activate myosin ATPase, chelate copper, and enhance copper uptake • β-Alanyl-imidazole – buffers the pH of anaerobically contracting skeletal muscle. • Homocarnosine – in human brain • Phosphorylated Serine, Threonine, & Tyrosine – Regulate the activity of certain enzymes • Lipid and carbohydrate metabolism • Properties of proteins • Signal transduction Methionine • Source of methyl groups • Polyamines – Spermine & spermidine Cysteine • Coenzyme A – Thioethanolamine • Taurine conjugates – Taurocholic acid Histidine • Histamine – aromatic L-amino acid decarboxylase • Histidine compounds – ergothioneine, carnosine, and dietary anserine Compounds related to histidine. Ornithine & Arginine • Arginine – Formamidine donor • Creatine synthesis – Putrescine, spermine, and spermidine • via ornithine • The precursor of Nitric oxide (NO) – Neurotransmitter – Smooth muscle relaxant, and vasodilator Polyamines • Spermidine & spermine – Growth factors • for cultured mammalian cells – Stabilize • Intact cells • Subcellular organelles • Membranes – Hypothermic & hypotensive • Associate readily with DNA and RNA • L-Ornithine – Putrescine • Spermidine – Spermine Tryptophan • Serotonin (5-hydroxytryptamine) – Vasoconstrictor & stimulator of smooth muscle contraction. – Catabolism • MAO – 5-hydroxyindoleacetate – Carcinoid (argentaffinoma) • Overproduce serotonin • Urinary metabolites – N-acetylserotonin glucuronide – glycine conjugate of 5-hydroxyindoleacetate Tryptophan • Melatonin – N-Acetylation of serotonin – O-methylation – Rapidly metabolized • Hydroxylation – Conjugation • Urinary catabolites (tryptophan) – 5-hydroxyindoleacetate and indole 3-acetate • Thyroid hormone Conversion of tyrosine to epinephrine and norepinephrine in neuronal and adrenal cells Creatinine Biosynthesis and metabolism of creatine and creatinine γ-Aminobutyrate • Inhibitory neurotransmitter Metabolism of γ-aminobutyrate
