On the Relationship between Rate of ATP Synthesis and H⁺ Electrochemical Gradient in Rat‐Liver Mitochondria

Abstract

The relationship between rate of ATP synthesis, JATp, and value of the proton electrochemical gradient, A f i~ has been analyzed in intact mitochondria.Onset of phosphorylation causes a depression of AfiH of 1.5 kJ/mol. There is a close parallelism between inhibition of &rp and restoration of A i H to its state-4 value during titrations with oligomycin or atractyloside.Titrations The consistence of the present data with either a chemiosmotic model where AFH is the sole and obligatory intermediate for energy coupling, or models where there is a direct transfer of energy between the two pumps is discussed.In mitochondria, bacteria and chloroplasts, e-transfer and ATP hydrolysis occur through the operation of H + pumps, which create a H + electrochemical gradient, A~H , between outer medium and inner space [l]. ATP synthesis is generally thought to occur through a back-to-back coupling of the two H i pumps. The mechanism proposed by Mitchell [2,3], known as the chemiosmotic hypothesis, assumes that coupling between redox and ATP-driven H + pumps is achieved through a delocalized A,& between the bulk aqueous phases and involves a H'-catalyzed reaction at the active site of the ATPase.Other views, although recognizing the fundamental role of protons, differ principally with respect to the molecular mechanisms and to the role of bulk phase A j H . According to Williams [4] the protons are generated in membrane-controlled spaces, not in equilibrium with one another, and the energized protons are trapped locally to drive ATP synthesis. AfiH represents an energy storage rather than an intermediate in coupling [4,5]. In the hypothesis called 'localized chemiosmosis' [6], domains are assumed where H + ions do not freely equilibrate with the bulk phase and where a A,CH higher than in bulk phase is established (cf. also [5,7,28]). Conformational changes of the ATPase are required, in the alternating site model of Boyer [9], for the utilization of A&. However it is doubtful whether these changes are due to the establishment of A f i~ or to protein-protein interactions in the membrane. AfiH-independent mechanisms have also been proposed by others (e.g. [lo-121).ATP synthesis can be driven by an artificial bulk-phase AfiH gradient in mitochondria, submitochondrial particles, Abbreviutions. CF30PhzC(CN)2, carbonylcyanide p-fluoromethoxyphenylhydrazone; Ph3MeP+, triphenylmethylphosphonium; Mops, 4-morpholinepropanesulfonic acid: Ap5A, adenosine(5')pentaphospho-(5')adenosine; J,, electron flow; Ah, electron flow in static head (state 4).chloroplasts and liposomes inlaid with the ATPase sythase complex [13-171. This is compatible with the views that ATP synthesis may be due either exclusively to a H + current through a protonic pathway reaching the FI-active site or to AiH-induced conformational changes coordinated with H + translocation at different sites.If the bulk-phase A& is the sole intermediate coupling the two H + pumps, some quantitative relationship between the rate of ATP synthesis, JATp, and A& is expected. One predicti...

Relationships of respiratory chain and ATP‐synthetase in energized mitochondria

“…These results were recently confirmed in [3]. Authors in [4] observed this effect with submitochondrial particles.…”

Multiple relationships between rate of oxidative phosphorylation and Δµ̃H in rat liver mitochondria

“…The former apparently exhibit only one JAT~ vs APH relationship [9] while the latter show several [1,2]; this paper). An analogous difference might exist between chloroplasts [5] and bacterial chromatophores [3,4].…”

The mechanism of the conservation of energy of biological oxidations

“…Zoratti et al [93] also considered protein-protein interaction as one possible explanation of their experimental results. The direct-collision hypothesis differs from those involving localized protons or localized AfiH +, which require a 'pool' of protons, albeit maybe a small one [32,941, functioning between the two enzymes.…”

“…[93]). In consequence, the concentration of uncoupler needed is related only to the concentration of the interacting enzymes concerned in the energy transduction.…”