Oxidative deamination of S-adenosyl-L-homocysteine by rat kidney L-amino acid oxidase.

Cell-free extracts prepared from rat kidney or liver catalyzed the oxidative deamination of S-adenosyl-Lhomocysteine to S-adenosyl-y-thio-a-ketobutyrate. This reaction was found to be catalyzed by L-amino acid oxidase (L-amino acid:oxygen oxidoreductase (deaminating), EC 1.4.3.2). In the presence of catalase, 0.48 pmole of oxygen was consumed for each micromole of substrate oxidized, and 1 pmole each of S-adenosyl-y-thio-a-ketobutyrate and ammonia were formed. In the absence of catalase oxygen consumption was doubled. The pH optimum for S-adenosyly-thio-a-ketobutyrate formation ranged from 8.8 to 9.2 and the K, value for S-adenosyl-L-homocysteine was 2.48 x lo-% M. At substrate concentrations of 10 mM and at pH 9.0, the ratio of specific activities with S-adenosyl-L-homocysteine to that with L-leucine or with L-methionine was 0.31 and 0.41, respectively. Partially purified L-amino acid oxidase was also found to be active with L-homocysteine and S-adenosyl-~methionine.