Affiliation:
1. Department of Biochemistry, Medical School, University of Bristol, Bristol BS8 1TD, U.K.
Abstract
1. Pi competitively inhibited succinate oxidation by intact uncoupled mitochondria in the presence of sufficient N-ethylmaleimide to block the phosphate carrier, with a Ki of 2.5mm. 2. Of a large number of phosphate esters and phosphonate compounds, phenyl phosphate and phenylphosphonate were found to inhibit competitively uncoupled succinate oxidation by intact but not broken mitochondria. By comparison, benzoate was a relatively weak competitive inhibitor of succinate oxidation by intact mitochondria but a relatively potent inhibitor of succinate dehydrogenase. 3. Phenyl phosphate and phenylphosphonate were non-penetrant, and inhibited Pi-dependent swelling of mitochondria suspended in isosmolar ammonium malate in a manner non-competitive with Pi. The inhibitors did not affect mitochondrial swelling when tested with Pi alone. 4. It is concluded that: (i) phenyl phosphate and phenylphosphonate behaved as non-penetrant analogues of Pi, since their inhibitory properties were in strict contrast with those of benzoate; (ii) phenyl phosphate and phenylphosphonate interacted with the dicarboxylate carrier but not with the phosphate carrier; (iii) Pi was effective as a competitive inhibitor of succinate oxidation because of its being either an alternative substrate for the dicarboxylate carrier or competitive with succinate for the intramitochondrial cations as proposed by Harris & Manger (1968).
Cited by
15 articles.
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