Respiration-driven proton translocation in rat liver mitochondria

Abstract

1. Pulses of acidity of the outer aqueous phase of rat liver mitochondrial suspensions induced by pulses of respiration are due to the translocation of H+ (or OH−) ions across the osmotic barrier (M phase) of the cristae membrane and cannot be attributed to the formation (with acid production) of a chemical intermediate that subsequently decomposes. 2. The effective quantity of protons translocated per bivalent reducing equivalent passing through the succinate-oxidizing and β-hydroxybutyrate-oxidizing spans of the respiratory chain are very close to 4 and 6 respectively. These quotients are constant between pH5·5 and 8·5 and are independent of changes in the ionic composition of the mitochondrial suspension medium provided that the conditions permit the accurate experimental measurement of the proton translocation. 3. Apparent changes in the →H+/O quotients may be induced by conditions preventing the occurrence of the usual backlash; these apparent changes of →H+/O are attributable to a very fast electrically driven component of the decay of the acid pulses that is not included in the experimental extrapolations. 4. Apparent changes in the →H+/O quotients may also be induced by the presence of anions, such as succinate, malonate and phosphate, or by cations such as Na+. These apparent changes of →H+/O are due to an increase in the rate of the pH-driven decay of the acid pulses. 5. The uncoupling agents, 2,4-dinitrophenol, carbonyl cyanide p-trifluoromethoxyphenylhydrazone and gramicidin increase the effective proton conductance of the M phase and thus increase the rate of decay of the respiration-driven acid pulses, but do not change the initial →H+/O quotients. The increase in effective proton conductance of the M phase caused by these uncouplers accounts quantitatively for their uncoupling action; and the fact that the initial →H+/O quotients are unchanged shows that uncoupler-sensitive chemical intermediates do not exist between the respiratory-chain system and the effective proton-translocating mechanism. 6. Stoicheiometric acid–base changes associated with the activity of the regions of the respiratory chain on the oxygen side of the rotenone- and antimycin A-sensitive sites gives experimental support for a suggested configuration of loop 3.

Sodium/Proton antiporter of rat liver mitochondria

“…Mitchell [ 111 first proposed that exchange of protons for monovalent cations was involved in regulation of ApH between the mitochondrial matrix and cytosol. Cations such as Na+ increased the rate of decay of proton gradients established by electrogenic proton translocation through the electron transport chain, suggesting the existence of a Na'/H+ antiporter [8]. Similar conclusions were reached for both rat liver and bovine heart mitochondria by observing the passive swelling of mitochondria in the presence of various cations [10,12,13].…”

Proton‐coupled hexose transport in Chlorella vulgaris

“…The immediate sugar-specific alkalinization of the external medium was observed when respiration or when photosynthesis was driving sugar uptake. It is improbably, therefore, that changes of the pH-gradient brought about by organelles (mitochondria or chloroplast) and induced by the energy demand for sugar transport, has caused the apparent proton uptake from the medium, since pH-change generated by the chloroplast membrane is opposite to that of the mitochondrion [8,9]. The stoichiometry of protons taken up per sugar taken up seems equal under respiratory and photosynthetic conditions.…”

Mitochondrial respiratory chain dysfunction: Implications in neurodegeneration

“…The first four redox complexes (complexes I to IV) constitute the respiratory chain (RC), which transfers electrons from NADH and FADH 2 to molecular oxygen, the terminal electron acceptor. The energy released by the oxidation of these substrates is used to generate a proton gradient across the mitochondrial inner membrane that will be used by complex V for the synthesis of ATP (Reid et al, 1966;Mitchell and Moyle, 1967). Each of the OXPHOS complexes consists of multiple polypeptide subunits encoded either by nuclear or mitochondrial DNA (mtDNA), except for complex II that is exclusively encoded by the nuclear genome (nDNA).…”