ダイコン幼植物体における4-チオウリジン代謝生成物のペルオキシダーゼによる酸化

Peroxidase (1.11.1.7) purified from Japanese-radish (Raphanus sativus) seedlings catalyzed the oxidation of 4-thiouridine, a sulfur-containing nucleoside, to 4-thiouridine disulfide in the presence of H_2O_2. 4-Thiouridine-metabolites such as 4-thiouracil, 4-thio-UMP, 4-thio-UDP, 4-thio-UTP and 4-thio-UDP glucose also were the substrate of the peroxidase reaction. Acidic peroxidase isoenzymes were mainly responsible for the 4-thiouridine oxidation. An increased 4-thiouridine-oxidase activity in the seedlings germinated and grown with the nucleoside was observed. These result suggest that the oxidation of 4-thiouridine and of its metabolites by peroxidase is not beyond the bounds of possibility in 4-thiouridine-cultured radish seedlings.