Studies on Kojic Acid Metabolism by Microorganisms

Abstract

An enzymatic oxidation of kojic acid to comenic aldehyde was found in the decomposition process of kojic acid by Arthrobacter ureafaciens strain (K-l), a kojic acid decomposing bacteria. This enzyme was (probable a new type of non-heme iron protein) is assumed to catalyze the dehydrogenation of kojic acid, while the ferric ion contained in the enzyme is considered to serve as an acceptor of hydrogen released from kojic acid. The resulted ferrous ions are oxidized either by molecular oxygen under aerobic conditions or by NAD under anaerobic conditions, accompanying hydrogen peroxide in the former and reduced NAD in the latter. The enzyme was partially purified by using ammonium sulfate precipitation, gel filtration on Sephadex G-200 column and column chromatography with DEAE-Sephadex A-50. The activity increased to 85 fold, compared with crude extracts and the recovery of the activity was 33.9%. The optimum pH of the reaction was 7.75. The enzyme was inactivated by PCMB, and unstable upon heat treatment. A loss of about 50% of the activity was caused by heating at 35°C for 5min, but some reducing agents protected the enzyme from PCMB inhibition and the heat inactivation. Not only kojic acid, but also benzyl kojic acid or 5-methoxy kojic acid may be substrates. Km value for kojic acid was 1.43×10-5M. The molecular weight of the enzyme was estimated to be about 55, 000 and the enzyme contained about two atoms of iron in one molecule. The reaction mechanism for kojic acid oxidase is discussed.