Due to which of the following enzyme deficiency, vitamin C cannot be synthesised in humans?
(A) L-Glucuronic acid oxidase (B) L-Gulonic acid reductase (C) L-Gulonolactone oxidase (D) L-Gulonolactone reductase
(C) L-Gulonolactone oxidase produces Vitamin C Uronic acid pathway, but only in plants & most animals. Humans cannot make vitamin C due to absence of L-Gulonolactone oxidase enzyme.(See fig) Uronic acid pathway- glucose is conveed to glucuronic acid, pentoses and, in some animals, to ascorbic acid (not in man). ADDITIONAL EDGE: Uronic Acid Pathway synthesize Glucuronic Acid, Pentoses and Vit C Uses of Glucuronic acid: Incorporated into proteoglycans (Glucuronate used) Acts as a conjugating agent (Phase II conjugation reactions like bilirubin conjugation)