Abstract
Cell-free extracts of Mycoplasma pneumoniae showed two distinct reduced nicotinamide adenine dinucleotide (NADH(2)) oxidase activities in the supernatant fraction. By ammonium sulfate fractionation and polyacrylamide gel electrophoresis, one activity not requiring flavine co-factors was precipitated by 50 to 70% ammonium sulfate concentration and identified with a slower-moving band on acrylamide gel electrophoresis; a second NADH(2) oxidase activity was flavine mononucleotide (FMN) dependent and associated with a more rapidly moving band; it could only be partially precipitated by ammonium sulfate concentrations ranging from 50 to 100%. Studies with alternate electron acceptors indicated the presence of a menadione, a 2,6-dichlorophenol indophenol and a very weak ferricyanide oxido-reductase activity, but no cytochrome c oxido-reductase, in the cell-free preparations. The NADH(2) oxidase activities of all fractions were relatively cyanide insensitive and were only minimally inhibited by flavoprotein and other respiratory chain inhibitors. H(2)O(2) formation was negligible unless FMN, but not flavine adenine dinucleotide (FAD), was added to the crude NADH(2) oxidase system; upon fractionation and electrophoresis, the H(2)O(2) formation was associated with the FMN-dependent, more rapidly moving NADH(2) oxidase band. This FMN-dependent NADH(2) oxidase-H(2)O(2) generating system may be a mechanism for the H(2)O(2) formation observed during glucose oxidation in the intact organism.