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- L -homocysteine to S-adenosyl-γ-thio-α-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 µmole of oxygen was consumed for each micromole of substrate oxidized, and 1 µmole each of S-adenosyl-γ-thio-α-ketobutyrate and ammonia were formed. In the absence of catalase oxygen consumption was doubled. The pH optimum for S-adenosyl-γ-thio-α-ketobutyrate formation ranged from 8.8 to 9.2 and the Km value for S-adenosyl- L -homocysteine was 2.48 × 10−2 M . At substrate concentrations of 10 m M 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- L -methionine.