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Transmethylation of Homocysteine to Methionine: Efficiency in the Rat and Chick

Department of Animal Sciences, University of Illinois, 317 Mumford Hall, 1301 West Gregory Drive, Urbana, IL 61801

Experiments were conducted with young chicks and rats to quantify the efficacy of L-homocysteine as a methionine precursor. Linear growth responses were obtained to both L-methionine and L-homocysteine when added to a methionine-deficient intact-protein diet containing a plethora of cystine. Slope-ratio multiple regression methodology indicated L-homocysteine to be 64.5% as efficacious as L-methionine in rats and 62.5% as efficacious in chicks. Plasma-free methionine also increased linearly as graded levels of either L-methionine or L-homocysteine were added to the diet of rats. At higher dosages of L-homocysteine, betaine, but not choline, showed some efficacy in enhancing the conversion of homocysteine to methionine. In the linear response surface of the growth curve, however, supplemental betaine was without effect on L-homocysteine bioefficacy, as was also the case for supplemental sarcosine and N⁵-methyltetrahydrofolic acid.

KEY WORDS: • chicks • rats • methionine • cysteine • homocysteine • plasma methionine • betaine • choline • methionine precursor role of homocysteine

Manuscript received 4 February 1985. Revision accepted 12 June 1985.

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