Pyridoxine deficiency leads to altered metabolism of?
ANSWER: (B) TryptophanREF: Harper 27th ed chapter 29Tryptophan is degraded to amphibolic intermediates via the kynurenine-anthranilate pathway. Tryptophan oxygenase (tryptophan pyTrolase) 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 (pyridoxine) 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.
Phenylalanine
Tryptophan
Methionine
Tyrosine
Amino Acid Metabolism