The apparent independence of the phosphorylation and water formation reactions from the oxidation reactions of oxidative phosphorylation
Boyer, P.D.; Bieber, L.L.; Mitchell, R.A.; Szabolcsi, G.
Journal of Biological Chemistry 241(22): 5384-5390
ISSN/ISBN: 0021-9258 PMID: 5954804 Accession: 025681149
Relationships of the oxidation reactions to the phosphorylation and the water formation reactions of oxidative phosphorylation have been assessed by measurement of inhibitor effects on the PiATP, PiHOH, and ATPHOH exchange reactions. With mitochondria or with mitochondrial particles, additions of cyanide, Amytal, rotenone, or antimycin, with or without substrate addition, had no or only partial inhibitory effects on all exchanges. Particles oxidizing succinate or reduced diphosphopyridine nucleotide without added adenine nucleotides showed no detectable PiHOH exchange. The conclusion is reached that the phosphorylation and the water formation reactions probably occur without concomitant oxidation or reduction. Some additive effects of combinations of respiratory inhibitors on the exchanges were noted. This might reflect nonspecific inhibitions, or possibly a compulsory coupling of the phosphorylation or water formation reactions to formation of combinations with or changes in conformation of respiratory components. Any such combination required most likely occurs with a reduced form of the respiratory carrier. A fat-soluble iron chelator, 4,4,4-triflouro-1-(2-thienyl)-1,3-butanedione, and p-mercuribenzoate were noted to have roughly similar effects in promoting ATPase, in inhibiting succinate but not DPNH [reduced diphosphopyridine nucleotide] oxidation, and in uncoupling phosphorylation from oxidation. The chelator effects were readily reversible. Emphasis is given to the important point that the apparent independence of the water formation reaction from the oxidation reactions of oxidative phosphorylation is difficult to reconcile with many schemes for oxidative phosphorylation.