The Utilization by Vitamin B12-Deficient Chicks of Monomethylaminoethanol, Homocystine and Betaine as Precursors of Choline and Methionine

Abstract

Vitamin B₁₂-depleted chicks were fed a diet deficient in choline and methionine and lacking in vitamin B₁₂. Supplementation with monomethylaminoethanol, homocystine and betaine was compared to choline and methionine at equimolar concentrations, both in the presence and absence of vitamin B₁₂. The vitamin B₁₂-depleted chicks were able to utilize monomethylaminoethanol plus betaine and homocystine plus betaine just as effectively as equimolar concentrations of dietary choline and methionine. These results showed, therefore, that vitamin B₁₂ is not required for transmethylation in this species. In the absence of sufficient betaine to methylate adequately the precursors of choline or methionine, vitamin B₁₂ gave a marked growth response indicating it is required in the synthesis of methyl groups in chicks. Betaine appeared to supply methyl groups for other metabolic functions in lieu of those synthesized by vitamin B₁₂ when added to a diet deficient in methionine and vitamin B₁₂ in excess of the quantity required to methylate the precursors of choline.