Enzymatic oxidation of rifamycins by a microorganism of the genus Humicola

Abstract

The catalytic properties of partially purified rifamycin oxidase produced intracellularly by a strain of Humicola spp. (ATCC 20620) were investigated. The enzyme was most specific for rilamycin B among the various rifamycin derivatives tested. Its Km value for this substrate was 0.05 mM. Substrate inhibition was observed at substrate concentrations above 2 mM. Polyol compounds such as /)-hydroxy phenoxy acetic acid, 夕-hydroquinone，and cathecol were moderately oxidized by this enzyme. A pH of 7.8 and a temperature of 45CG were optimal for the enzyme activity. It was severely inhibited by Fe* and Hg*, but was not affected by other metal ions. As an enzyme source for industrial applications, whole cell preparations of the microorganism were tested. A time lag in the conversion-time profile was observed at the initial stage ol the reaction with whole cell enzyme, while no such a trend was detected with acetone-dried whole cells. The cell mernbrane may exert a difTusional barrier to the molecules of substrate and products. Delipidation of the cell membrane by acetone treatment was therefore advised, especially when a whole cell preparation of the enzyme was to be used for oxidation of rifamycins.