Partial Purification and Mechanism for the Inhibition by Various Salts of Ascorbate Oxidase in Vigna radiata Sprouts

Abstract

Ascorbate oxidase (AAO, EC1.10.3.3.) is widely distributed in plants, and is responsible for the oxidation of ascorbate during the storage and processing of vegetables. AAO of Vigna radiata was purified by DE-52 cellulose column chromatography and hydroxylapatite column chromatography. SDS-PAGE showed that AAO had been purified to a main band of 67 kDa. The optimum pH value was 4.95, and the K_m value for ascorbic acid was 1.25 × 10^-4m. The enzyme activity was inhibited by salts, the order of effectiveness being sodium citrate >NaCl>KCl>sodium malate>NH₄Cl> (NH₄) ₂SO₄. Sodium citrate and NaCl inhibited the enzyme activity non-competitively with K_i values of 50 mm and 130 mm, respectively.