Respiration-driven proton translocation in Micrococcus denitrificans.

The polarity and stoichiometry of respiration-driven proton translocation was studied by electrometric and spectrophotometric techniques inMicrococcus denitrificans in the context of the energy transduction mechanism in bacterial oxidative phosphorylation. 1. Protons are ejected through the plasma membrane during respiratory pulses and thereafter diffuse slowly back. 2. In presence of ionic species mobile across the membrane (K+-valinomycin, K+-gramicidin, or SCN−), limiting→H+/O quotients of 8 were obtained with endogenous respiratory substrates, and the rate of translocation (14·3 μg ions of H+/sec g cell dry weight) was commensurate with that of respiration optimally stimulated by FCCP at an →H+/O quotient of 8. 3. The rate of decay of the proton pulses was greatly increased by FCCP, but there was little or no effect on the →H+/O quotient characteristic of the respiratory system. 4. Various interpretations of the observations are discussed, and it is concluded that respiration is probably coupled directly or indirectly to electrogenic proton translocation. The observations are compatible with the chemiosmotic hypothesis of coupling between respiration and phosphorylation.