Melatonin is synthesized from which of the following amino acid?

Ans. A. Tryptophan. (Ref. Harper's Biochemistry 27th/Chapter 30; 26th/pg. 256)Conversion of Amino Acids to Specialized Products:# Glycine participates in the biosynthesis of heme, purines, and creatine and is conjugated to bile acids and to the urinary metabolites of many drugs.# In addition to its roles in phospholipid and sphingosine biosynthesis, serine provides carbons 2 and 8 of purines and the methyl group of thymine.# S-Adenosylmethionine, the methyl group donor for many biosynthetic processes, also participates directly in spermine and spermidine biosynthesis.# Glutamate and ornithine form the neurotransmitter -aminobutyrate (GABA).# The thioethanolamine of coenzyme A and the taurine of taurocholic acid arise from cysteine.# Decarboxylation of histidine forms histamine, and several dipeptides are derived from histidine and -alanine.# Arginine serves as the formamidine donor for creatine biosynthesis, participates in polyamine biosynthesis, and provides the nitrogen of nitric oxide (NO).# Important tryptophan metabolites include serotonin and melatonin.6# "tyrosine forms both epinephrine and norepinephrine, and its iodination forms thyroid hormone.Tryptophan.Tryptophan is degraded to amphibolic intermediates via the kynurenine-anthranilate pathway. Tryptophan oxygenase (tryptophan pyrrolase) opens the indole ring, incorporates molecular oxygen, and forms N-formylkynurenine. An iron porphyrin metalloprotein that is inducible in liver by adrenal corticosteroids and by tryptophan, tryptophan oxygenase is feedback- inhibited by nicotinic acid derivatives, including NADPH. Hydrolytic removal of the formyl group of N- formylkynurenine, catalyzed by kynurenine formylase, produces kynurenine. Since kynureninase requires pyridoxal phosphate, excretion of xanthurenate in response to a tryptophan load is diagnostic of vitamin B6 deficiency. Hartnup disease reflects impaired intestinal and renal transport of tryptophan and other neutral amino acids. Indole derivatives of unabsorbed tryptophan formed by intestinal bacteria are excreted. The defect limits tryptophan availability for niacin biosynthesis and accounts for the pellagra-like signs and symptoms.Amino acid derivatives: