A novel l‐glutamate oxidase from Streptomyces endus

Abstract

A new flavoenzyme using molecular oxygen to oxidize l-glutamic acid has been purified to homogeneity, as judged by polyacrylamide gel electrophoresis, from the culture medium of Streptomyces endus. Hydrogen peroxide, 2-oxoglutaric acid and ammonia are formed as products. Among 25 amino acids tested including d-glutamic acid, l-glutamine and l-aspartic acid, only l-glutamic acid is converted. The molecular mass of the enzyme was estimated to be about 90 kDa by gel chromatography and 50 kDa by SDS/PAGE. The subunit contains 1 molecule noncovalently bound FAD. The absorption spectrum shows maxima at 273, 355 and 457 nm and the isoelectric point is at pH 6.2. The K_m value for l-glutamic acid in air-saturated phosphate pH 7.0 was estimated to be 1.1 mM, the K_m for oxygen was calculated to be 1.86 mM at saturating concentration of l-glutamic acid. The enzymic reaction is inhibited by Ag⁺ and Hg²⁺ ions. The enzyme described here distinctly differs from two microbial l-glutamate oxidases purified hitherto, with regard to extremely high substrate specificity and to the subunit structure.