Oxidation of the S-methyl group by rat tissue preparations

An enzymic activity was detected in cell-free preparations of rat tissues capable of oxidizing the methyl group of l-methionine and other S-methyl compounds to CO 2. A stable powder was prepared from the supernatant fluid of a 50,000 g centrifugation of rat liver homogenates. A variety of labeled S-methyl compounds were oxidized by this preparation, and the pH optimum range, Km, and extents of reaction were determined for each compound. The enzyme activity was stimulated by additions of NAD and NADP and inhibited particularly by sulfhydryl compounds, sodium azide, and hydroxylamine. It is suggested that a peroxidative mechanism is involved in the oxidation of S-methyl groups to CO 2.