Studies on the in vivo Utilisation and the in vitro Enzymatic Reduction of Methionine Sulphoxide in Rats and Rat Tissues

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Abstract
The aim of this study was to gather information on the utilization of methionine sulfoxide as a source of methionine in the rat, and to find out where and to what extent reduction of methionine sulfoxide takes palce. Carcass analysis of rats fed methionine sulfoxide and cystine as the only S containing amino acids showed that methionine was formed. This is taken as evidence for reduction and utilization of methionine sulfoxide in rats. Enzymatic reduction of methionine sulfoxide in different rat tissues was not detected using various reducing agents and assay conditions. Bacteria reduced methionine sulfoxide with eventual secretion of methionine into the medium. The reduction was stereospecific as only L-methionine-l-sulfoxide was reduced. Weight gain and content of methionine sulfoxide in blood plasma and intestine were similar in rats fed in the presence or absence of antibiotics, indicating that bacteria in the intestine were not responsible for the utilization of methionine sulfoxide in the rat.