Stimulation of respiration-linked proton efflux in Escherichia coli by carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP)

A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

Oxidative phosphorylation by membrane vesicles from Bacillus alcalophilus

ADP and Pi-loaded membrane vesicles from t-malate-grown Bacillus alcalophilus synthesized ATP upon energization with ascorbate/N,N,N',N'-tetra-methyl-P-phenylenediamine. ATP synthesis occurred over a range of external pH from 6.0 to 11.0, under conditions in which the total protonmotive force delta-mu-H+ was as low as -30 mV. The phosphate potentials (delta Gp) were calculated to be 11 and 12 kcal/mol at pH 10.5 and 9.0, respectively, whereas the delta-mu-H+ values in vesicles at these two pH values were quite different (-40 +/- 20 mV at pH 10.5 and -125 +/- 20 mV at pH 9.0). ATP synthesis was inhibited by KCN, gramicidin, and by N,N1-dicyclohexylcarbodiimide. Inward translocation of protons, concomitant with ATP synthesis, was demonstrated using direct pH monitoring and fluorescence methods. No dependence upon the presence of Na+ or K+ was found. Thus, ATP synthesis in B. alcalophilus appears to involve a proton-translocating ATPase which functions at low delta-mu-H+.