Harpers

CONVERSION OF AMINO ACIDS TO SPECIALIZED PRODUCTS / 269SUMMARY• In addition to their roles in proteins and polypeptides,amino acids participate in a wide variety of additionalbiosynthetic processes.• Glycine participates in the biosynthesis of heme,purines, and creatine and is conjugated to bile acidsand to the urinary metabolites of many drugs.• In addition to its roles in phospholipid and sphingosinebiosynthesis, serine provides carbons 2 and 8 ofpurines and the methyl group of thymine.• S-Adenosylmethionine, the methyl group donor formany biosynthetic processes, also participates directlyin spermine and spermidine biosynthesis.• Glutamate and ornithine form the neurotransmitterγ-aminobutyrate (GABA).• The thioethanolamine of coenzyme A and the taurineof taurocholic acid arise from cysteine.• Decarboxylation of histidine forms histamine, andseveral dipeptides are derived from histidine andβ-alanine.• Arginine serves as the formamidine donor for creatinebiosynthesis, participates in polyamine biosynthesis,and provides the nitrogen of nitric oxide(NO).• Important tryptophan metabolites include serotonin,melanin, and melatonin.• Tyrosine forms both epinephrine and norepinephrine,and its iodination forms thyroid hormone.REFERENCEScriver CR et al (editors): The Metabolic and Molecular Bases ofInherited Disease, 8th ed. McGraw-Hill, 2001.