THE DIRECTION OF THE PROTON-EXCHANGE ASSOCIATED WITH THE REDOX REACTIONS OF MENAQUINONE DURING ELECTRON-TRANSPORT IN WOLINELLA-SUCCINOGENES

Wolinella succinogenes (after treatment with EDTA) or inverted vesicles of the bacterial membrane catalyzed the reduction of the water-soluble MK-analogue 2,3-dimethyl-1,4-naphthoquinone (DMN) by H-2. DMN reduction was associated with the generation of an electrochemical proton potential (dp) across the membrane. In the absence of a Delta psi, the amount of protons liberated by the bacteria was 0.59 per electron transferred from H-2 to DMN, while 0.46 protons were consumed from the external medium by the inverted vesicles. The reduction of DMN by formate catalyzed either by the bacteria or liposomes containing formate dehydrogenase, caused the uptake of tetraphenylphosphonium (TPP) which was reversed by a protonophore. DMNH(2) oxidation by fumarate catalyzed by bacteria, inverted vesicles or liposomes containing fumarate reductase, was not associated with the accumulation of either TPP or tetraphenylboranate (TPB). The results are interpreted to indicate that the protons required in DMN reduction to DMNH(2) are taken up from the bacterial cytoplasm, and those released in the reverse reaction are liberated into the cytoplasm. The same is also likely to apply to the redox reactions of the bacterial MK and MKH(2). The results confirm the hypothesis that the electrochemical proton potential generated by fumarate reduction with H-2 or formate is caused by transmembrane electron transport. The redox reactions of MK and MKH(2) which are involved in the electron transport are not associated with proton translocation across the membrane.