A coulombic hypothesis of mitochondrial oxidative phosphorylation

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.

NMR, calorimetric, spin-label, and optical studies on a trifluoromethyl-substituted styryl molecular probe in dimyristoylphosphatidylcholine vesicles and multilamellar suspensions: a model for location of optical probes

NMR, calorimetric, and optical spectroscopic studies have been performed on a trifluoromethyl-substituted styryl molecular probe bound to vesicles and multilamellar suspensions formed from dimyristoylphosphatidylcholine (DMPC). In the fluorine NMR spectrum at 35 degrees C there are two partially resolved resonances, but these collapse to an apparently single resonance at temperatures above 60 degrees C. However, a line-shape analysis is not consistent with exchange between two sites on an NMR time scale, and the two resonances are assumed to be due to probe sites in the inner and outer leaflets of the vesicles. Two fluorescence lifetimes, each associated with one of these sites, characterize the decay curves for the molecular probe bound to DMPC vesicles. The shift reagent Eu(FOD)3 and several nitroxide spin labels covalently bound to lipophilic structures strongly attenuate the lower frequency component of the fluorine NMR spectrum and also shift the other resonance to higher frequencies. The effect of two spin labels on the probe fluorine T2 relaxation time has been used to estimate the distance between the spin label unpaired electron and the trifluoromethyl group. The location of the spin label site in the membrane was determined from the effect of the unpaired electron on the lipid 13C linewidths. A model for the location of the probe in the bilayer was developed from the above information and refined using molecular mechanics calculations on a probe-DMPC lipid complex. The long axis of the probe parallels the bilayer normal; the styryl-group portion of the optical chromophore is located slightly below the glycerol backbone, and the remainder of the chromophore extends well into the hydrophobic region of the bilayer. Therefore, the optical properties of the probe should not be significantly influenced by alterations of the membrane surface charge density. Parameters derived from DSC studies in the gel-to-lipid crystal phase transition of DMPC are extremely sensitive to the probe. Even at 0.0001 mol fraction of probe, the transition is substantially broadened, and the delta H for the transition has increased, just as one predicts for the formation of a tight complex described above.

The coulombic hypothesis of mitochondrial energy transduction: an attempt to quantify relationships in the energized zones

From a consideration of (i) an assumed maximal respiration rate (ii) the ATP synthesis which can be obtained from mitochondria after respiratory inhibition and (iii) electrophoretic mobility data, the number of energized zones on the mitochondrial inner membrane has been assessed as 0.68 X 10(18)/g protein. For a single zone (representing one electron transport chain, three phosphorylating complexes and three fixed-charge cycles) in which all the cycles use molecular species doubly-charged in the energized form (b2-), the zone area will be 134 A2 and the specialized fixed charge concentration 4.5 X 10(-2) sigma/A2. The lifetime ("blink") of any energized form will be 24.4 ms, 5% of the cycle repeat time when a site 1 substrate is being oxidized.

Local energized proton hypotheses of mitochondrial oxidative phosphorylation

Two hypotheses are compared each interpreting mitochondrial energy transduction in terms of a localized form of proton activity. Their differences are seen to be profound and far-reaching. It is concluded that the "chemiosmotic/local energized proton dialogue" as conducted hitherto has offered a very incomplete and restricted analysis of the problems of mitochondrial oxidative phosphorylation.