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