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Importance of Sarcosine Formation in Methionine Methyl Carbon Oxidation in the Rat^1,2,

Departments of Nutritional Sciences and Meat and Animal Science, University of Wisconsin, Madison, Wisconsin 53706

Experiments in vitro using rat liver slices indicated that the incorporation of the methionine methyl carbon into sarcosine and serine was dependent upon available glycine and most probably involves glycine methyltransferase. Although the sarcosine methyl carbon was rapidly oxidized to CO₂, its formation accounted for only a small proportion of the oxidation of the methionine methyl carbon to CO₂ under these conditions. In vivo experiments using a sarcosine trapping pool with 0.3% to 3.0% L-[methy]-¹⁴C]methionine in the diet indicated that from 5% to 14% of the absorbed methionine methyl carbon was metabolized via sarcosine, and that this accounted for only 10% to 20% of the observed oxidation of the methyl carbon to CO₂. The adaptive response of the rat to high levels of dietary methionine, as indicated by greater oxidation of the methyl carbon to CO₂, is in part due to increased sarcosine synthesis. The failure of supplemental glycine to stimulate oxidation of the methionine methyl carbon to CO₂ in rats receiving 3% methionine plus 10% sarcosine may be due to sufficient glycine being produced from sarcosine metabolism.

KEY WORDS: • methionine • methyl groups • sarcosine • S-adenosylmethionine

¹ Research supported by funds from the College of Agricultural and Life Sciences. University of Wisconsin, the Graduate School, University of Wisconsin, and by Public Health Service Research Grant #AM 15227.

² Paper No. 687 from the Department of Meat and Animal Science.

³ Present address: Department of Pathology, Medical School, University of Wisconsin, Madison, Wisconsin 53706.

Manuscript received 29 January 1976.

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