[Generation of membrane potential by aerobic bacteria Micrococcus lysodeikticus. Correlation between coupled and...

The effects of cyanide and nonylhydroxyquinoline-N-oxide on membrane potential generation and oxidase activities in intact cells and membrane particles of M. lysodeikticus were studied. Low concentrations of the inhibitors interacting with the components of one branch of a branched respiratory chain of M. lysodeikticus strongly inhibit the membrane potential generation and only slightly reduce the total respiration rate. It was assumed that the generation of delta psi takes place in the b-c locus of the respiratory chain branch terminated with cytochrome oxidase; over 90% of total O2 uptake provides for the uncoupled respiration via cytochrome omicron. Inside the b-c locus two sites responsible for delta psi generation were singled out; these sites differ in their sensitivities towards nonylhydroxyquinoline-N-oxide. Based on the data obtained and the effect of "extra-reduction" of cytochrome b566 a hypothetical model of the respiratory chain of M. lysodeikticus was developed, which includes the branching of the electron flux to two terminal pathways and redox equivalent transport cyclization via the menaquinone cycle. The physiological role of uncoupled respiration through cytochrome omicron is discussed.