valinomycin and menadiol

Inside-out subcellular vesicles of Azotobacter vinelandii are found to produce delta pH and delta psi (interior acidic and positive) when oxidising malate or menadiol. These effects are inherent in both Cyd+ Cyo- (lacking the o-type oxidase) and Cyd- Cyo+ (lacking the bd-type oxidase) strains. They appear to be myxothiazol-sensitive in the Cyd- Cyo+ strain but not in the Cyd+ Cyo- strain. The H+/e- ratio for the terminal part of respiratory chain of a bd-type oxidase overproducing strain is established as being close to 1. It is also shown that NADH oxidation by the vesicles from the Cyd- Cyo+ strain is sensitive to low concentrations of myxothiazol and antimycin A whereas that of the Cyd+ Cyo- strain is resistant to these Q-cycle inhibitors. It is concluded that (i) the bd-type oxidase of A. vinelandii is competent in generating a protonic potential but its efficiency is lower than that of the o-type oxidase and (ii) Q-cycle does operate in the o-type cytochrome oxidase terminated branch of the A. vinelandii respiratory chain and does not in the bd-type quinol oxidase terminated branch. These relationships are discussed in the context of the respiratory protection function of the bd-type oxidase in A. vinelandii.

Topics: Anaerobiosis; Azotobacter vinelandii; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cell Fractionation; Cytochrome b Group; Cytochromes; Electron Transport Chain Complex Proteins; Escherichia coli Proteins; Hydrogen-Ion Concentration; Kinetics; Malates; Methacrylates; Oxidoreductases; Subcellular Fractions; Thiazoles; Valinomycin; Vitamin K