Abstract
The antioxidative activities of methionine and its related compounds with the autoxidation of linoleic acid were determined and the following results were obtained.
(1) The presence of 10-3 M of methionine in the reaction system of pH 6.0 was as effective as that of tryptophan with the antioxidative action. The antioxidative effect of methionine increased along with the increased concentration, and no significant change was observed over the range of pH 6 to 9.
(2) Methionine ethyl ester and benzoyl methionine, in which either carboxyl group or amino group of methionine was modified, prevented as efficiently as methionine the autoxidation of linoleic acid at pH 6.0, while benzoyl methionine ethyl ester masking both carboxyl-and amino-groups showed only slight antioxidative activity.
(3) The antioxidative activities of methionine sulfoxide, methionine sulfone and DL-aminobutyric acid were markedly lower than that of methionine. Moreover, the most part of methionine was trans-formed into methionine sulfoxide in the course of the reaction.
On the basis of the experimental results obtained, it was suggested that the antioxidative activity of methionine was caused by cooperative action of methylmercapto group and either free carboxyl-or amino-group.
