Effect of Glycine and Serine on Methionine Metabolism in Rats Fed Diets High in Methionine

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Abstract
Glycine and serine have previously been shown to alleviate the growth-depressive effect of consumption of excessive amounts of methionine. These supplements were not immediately effective, suggesting that some type of adaptation was required. Therefore, studies were initiated on the effect of the adaptation and of glycine and serine supplementation on the oxidation of methionine in vivo. The adaptation of rats to diets containing high levels of methionine involves an increased ability to convert both the methyl and carboxyl carbons of methionine to CO2. Supplementation of the high methionine diet with glycine or serine enhances methionine oxidation only after the adaptation. In adapted animals these supplements decrease the plasma concentration of methionine and increase the rate of stomach emptying, suggesting that the beneficial effect of adding glycine or serine to the high methionine diet is via an enhanced rate of methionine catabolism which results in lower blood concentrations of methionine and hence increased food consumption and growth.