Regulation of reductase formation in Proteus mirabilis

Abstract

Summary. The levels of several redox enzymes in a chlorate-resistant mutant of Proteus mirabilis, which is partially affected in the formation of formate hydrogenlyase, thiosulfate reductase and tetrathionate reductase, were compared with those of the wild type. The composition of the electron transport system of both strains was almost the same in cells grown aerobically, but very different in cells grown anaerobically. In the mutant, the cytochrome content increased twofold, whereas the level of the anaerobic enzymes is strongly diminished. The anaerobic formation of electron transport components in the mutant was, in contrast to that of the wild type, not influenced significantly by azide. During anaerobic growth with nitrate low levels of a functional nitrate reductase system were formed in the mutant. Under these conditions the formation of formate dehydrogenase, formate hydrogenlyase, formate oxidase, thiosulfate reductase, tetrathionate reductase, cytochromc ha83, 5 and partly that of cytochrome a 2, was repressed. The repressive effect of nitrate, however, was completely abolished by azide. Therefore, it seems likely that a functional nitrate reductase system, rather than nitrate, controls the formation of the enzymes repressible by nitrate.