Occurrence of L-Amino Acid Oxidase in the Marine Red Alga Gymnogongrus flabelliformis

Abstract

The L-amino acid oxidase of the marine red alga Gymnogongrus flabelliformis was partially purified and studied.
The enzyme was purified about 45-fold in a yield of 13% by means of acetone precipitation, gel filtration, and DEAE-Sephadex column chromatography. This enzyme had very limited specificity, catalyzing the oxidative deamination of basic L-amino acids and methionine. The relative activeties for the amino acids at pH 8.0 were as follows: 100 for L-gigartinine, 84 for L-arginine, 83 for L-ornithine, 54 for L-lysine, 29 for L-citrulline, 23 for L-histidine and 20 for L-methionine. D-Amino acids were not oxidized. L-Arginine, which was used as the substrate of the enzyme reaction was oxidized to equimolar amounts of α-keto acid and ammonia with consumption of equimolar oxygen. Hydrogen peroxide formation was also detected. These results led the authors to postulate that the enzyme is a kind of L-amino acid oxidase. The pH-activity curve had a relative broad maximum between pH 8.0 and 9.0. The optimum temperature was about 30°C. The enzyme activity was inhibited by the treatment of EDTA, but it was reactivated by some metal ions. Ca²⁺ was the most preferable. The occurrence of L-amino acid oxidase in marine algae is demonstrated for the first time.