Metabolism of d- and l-Methionine

Abstract

Previous investigation of the physiological rôle of methionine in the animal organism led the writers to conclude that “methionine, like cystine, is capable of unmistakably stimulating growth in albino rats subsisting on a basal diet poor in cystine. 1 , 2 It was pointed out 2 that this observation immediately raised various questions relative to the intermediary metabolism of methionine. Referring to one of these problems, we stated: “It is obvious, of course, that, since the addition of methionine (dl) to the diet of animals subsisting on the regimen previously described leads to growth stimulation, the study of the physiological behavior of …. the separate optically active forms of methionine becomes important. ”These compounds have been investigated with the following results.

Methionine was synthesized and resolved according to the methods of Windus and Marvel. 3 , 4 d-Methionine as well as the naturally occurring l-methionine stimulates growth in the rat ingesting our cystine-methionine deficient diet, (cf., the results of similar experiments on tryptophane and cystine. 5 , 6 , 7 , 8 The formyl derivatives of the 2 optical isomers of methionine also were tested. The administration of formyl l-methionine causes increments of body weight similar to those produced by both l- and d-methionine. On the other hand, formyl d-methionine apparently cannot be utilized by the animal organism for growth under the conditions of our experiments. Analogous observations have been made on the physiological availability of the acetyl derivatives of d- and l-tryptophane. 6