Effect of Dietary Vitamin B12 on Methionine Biosynthesis by Chick Liver Homogenates.

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Abstract
Chicks were fed a basal diet deficient in methionine and vitamin B12 other groups were given this basal diet supplemented with methionine and B12 singly and in combination. Growth was improved by B12 or methionine and the 2 in combination did not improve growth over that obtained by either nutrient separately. Homogenates of livers from chicks in each of the 4 groups were incubated with homocysteine and either formaldehyde C14 or formate C14. Methionine was isolated from the incubation mixture and its C14 content determined. Vitamin B12 treatment increased the conversion of formate C14 to methionine methyl and depressed the conversion of formaldehyde to methionine methyl. Dietary methionine exerted no significant effect on methionine biosynthesis. The results implicate vitamin B12 in the reduction of formate to formaldehyde, a reaction catalyzed by methylene tetrahydrofolic dehydrogenase.

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