The Effect on Growth and the Toxicity of the Two Isomers of Methionine

Summary. This paper reports the results of growth tests on young white rats on diets adequate in other respects but containing varying concentrations of L‐ and D‐methionine. The following results were obtained: The concentration required for maintenance of the body‐weight was 0.10 % L‐methionine and 0.12 % D‐methionine in the diet. The effect of the D‐methionine on the growth was merely 76–84 per cent, of that of the L‐methionine. Maximal growth was obtained at a concentration of 0.25–1% L‐methionine and of 0.5C–.2% D‐methionine in the diet. D‐methionine seems to be less toxic than L‐methionine. A toxic effect on the growth (stagnation in weight) resulted at a concentration of 3.5% L‐methionine and of 5.4% D‐methionine in the diet. In default of methionine in the diet the animals had a poor appetite, which immediately improved on the addition of L‐ or D‐methionine. A maximal appetite was obtained with 0.125–1% L‐methionine or 0.125–4% D‐methionine. With higher concentrations a decrease in appetite would appear.