D-Aminoaciduria in mutant mice lackingD-amino-acid oxidase activity.

Urine of mutant ddY/DAO(-) mice lackingD-amino-acid oxidase activity contained more serine and proline than that of normal ddY/DAO(+) mice.D-Amino-acid oxidase treatment of urinary amino acids decreased the serine and proline, suggesting that they containedD-isomers. An HPLC analysis confirmed the presence ofD-serine. Urinary serine and proline contents were not decreased when the ddY/DAO(-) mice were fed a diet which did not contain supplementaryD-methionine or when they were given water containing antibiotics. These results suggest that theD-serine andD-proline do not derive from theD-methionine supplemented in the diet or from intestinal bacteria. In urine of the ddY/DAO(-) mice, a substance which seemed to beD-methionine sulfoxide and/orD-methionine sulfone was present. It is probably a metabolite of theD-methionine supplemented in the diet. TheD-aminoaciduria in the mutant mice lackingD-amino-acid oxidase activity indicates that this enzyme is involved in the metabolism of theD-amino acids in normal mice.