Vitamin shunt activity

Kaplan and Basford (1976) in their study of neutrophil function in four patients with megloblastic anemia showed that resting levels of hexose monophosphate shunt activities were slightly lower in PMN leukocytes from patients with vitamin Bi2 deficiency. However, when challenged with the latex beads or staphylococci, HMPS activity was only 1/3 that of controls. There was no impairment in leukocytes from patients with folic acid deficiency. Microbicidal activity was also slightly decreased in... 

Thiamine pyrophosphate is a coenzyme and the active form of vitamin B. It functions as coenzyme in decarboxylation of a-keto acid and in hexose monophosphate shunt. 

Certain vitamins can be synthesized by humans in limited quantities. Niacin can be formed from tryptophan (Chapter 17). This pathway is not active enough to satisfy all the body s needs however, in calculating the RDA for niacin, 60 mg of dietary tryptophan is considered equivalent to 1 mg of dietary niacin. In Hartnup s disease (see Table 38-1 and Chapter 17), a rare hereditary disorder in the transport of monoaminomonocarboxylic acids (e.g., tryptophan), a pellagra-like rash may appear, suggesting that over a long period of time dietary intake of niacin is insufficient for metabolic needs. This pattern also occurs in carcinoid syndrome in which much tryptophan is shunted into the synthesis of 5-hydroxytryptamine. 

The addition of riboflavin to the system repeatedly caused a small but significant synthesis of cyanocobalamin. More efficient shunting of the synthesis toward cyanocobalamin took place when parts of the riboflavin molecule and related substances were added, e.g. l-amino-3,4-di-methyl-6-D-ribitylaminobenzene l,2-dimethyl-4,5-diaminobenzene and 5,6-dimethylbenzimidazole. These findings seem consistent with the view of Woolley (1951) that the metabolic paths of the two vitamins are closely interconnected. The activity of riboflavin itself in promoting the synthesis of cyanocobalamin need not of course imply that the vitamin is actually broken down to provide a precursor of cyanocobalamin nucleotide. It could equally well be that a common precursor of riboflavin and cyanocobalamin nucleotide is normally available in limiting amounts and is used preferentially in the synthesis of riboflavin. The provision of preformed riboflavin might then spare this precursor for the synthesis of cyanocobalamin. 

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