Enzymatic reduction of methionine sulfoxide: In vitro experiments with rat liver and kidney

Direct experimental evidence is given for the presence of methionine sulfoxide reducing enzymatic activity in rat liver and kidney. Experiments were performed with L(U. 14 C) methionine RS sulfoxide, incubated with liver or kidney homogenates or subcellular fractions, the formation of methionine being determined by ion-exchange chromatography and radioactivity measurement. The methionine sulfoxide reducing activity is thermolabile and enhanced by the addition of NADH to the incubation medium. The subcellular distribution patterns of the enzymatic activities from the liver and from the kidney are quite different.