Isolation, enzyme production and characterization of d-aspartate oxidase from Fusarium sacchari var. elongatum Y-105

A microorganism that produces d-aspartate-oxidizing enzyme by induction was isolated from soil, and identified as Fusarium sacchari var. elongatum Y-105. The enzyme catalyzed the oxidative deamination of d-aspartate (d-Asp) and produced oxaloacetate, ammonia, and hydrogen peroxide, stoichiometrically. The enzyme is designated "d-Asp oxidase" (EC 1.4.3.1). In addition to d-Asp, the enzyme oxidized d-glutamate (d-Glu) and N-methyl-d-aspartate (NMDA). N-Acetyl-d-Asp and other d- or l-amino acids, however, were inert as substrates. The optimum pH and temperature were 7.5 and 40°C, respectively. The enzyme was stable at pH 9.0 and temperature of 50°C, respectively. The enzyme activity was not inhibited by sodium benzoate which is a specific inhibitor of d-amino acid oxidase from mammals. The enzyme activity was also not affected by carboxylates such as meso- or d-tartarate, citrate, and fumarate which inhibit d-Asp oxidase from rabbits.