A lactate oxygenase from Mycobacterium phlei: II. Spectral characteristics in aerobic and anaerobic reactions

Abstract

Lactate oxygenase from Mycobacterium phlei (lactate oxidative decarboxylase) catalyzes the oxygenative conversion of l-lactate to acetate, but acts as an l-lactate dehydrogenase under anaerobic conditions, producing a stoichiometric amount of pyruvate. In an effort to obtain further information on the reaction mechanism, a stopped-flow spectrophotometric technique has been applied to both aerobic and anaerobic reactions of the enzyme. The flavin moiety (FMN) of the enzyme proceeds in a highly oxidized state during the steady state at low lactate and high oxygen concentrations. If the aerobic steady state is maintained at high lactate and low oxygen concentrations, a new spectral species, clearly distinguishable from that of the oxidized state, is visible partially. During anaerobic reduction of the flavin moiety with l-lactate, another species with a weak absorption band at a long wavelength region appears. The significance of these findings in terms of the catalytic reaction mechanism is discussed.