The H+/site ratio of mitochondrial electron transport

M. D. Brand, B. Reynafarje, A. L. Lehninger

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3 Scopus citations


The number of H+ ejected during passage of 2e- through each energy conserving site of the mitochondrial respiratory chain (the H+/site ratio) was measured in three ways. In each case transmembrane movements of endogenous phosphate were minimized. Measurement of the uptake of weak acids during loading of mitochondria with Ca2+ demonstrated that 2.0 weak acid anions were accumulated per Ca2+ ion. Since 1.7 to 2.0 Ca2+ ions were taken up per site, these data correspond to an H+/site ratio of 3.5 to 4.0. More direct measurement of H+ ejection using the oxygen pulse technique demonstrated that the H+/site ratio was 3.0. In these experiments phosphate movements were prevented by addition of N ethylmaleimide to inhibit phosphate hydroxide antiport, by washing the mitochondria to remove endogenous phosphate, or by working at 5°C to reduce the rate of phosphate transport. When phosphate movements were allowed, H+/site ratios of 2.0 were observed. Measurement of the initial steady rates of oxygen consumption and H+ ejection following addition of substrate to aerobic, substrate limited mitochondria yielded H+/site ratios of 2.0, which were elevated to 4.0 when phosphate transport was prevented as described above. Previous determinations of the H+/site ratio were thus underestimates due to the unrecognized movements of endogenous phosphate; the results show that the H+/site ratio is at least 3.0 and may be as high as 4.0.

Original languageEnglish (US)
Pages (from-to)595-602
Number of pages8
JournalJournal of Cellular Physiology
Issue number4
StatePublished - 1976

ASJC Scopus subject areas

  • Cell Biology
  • Clinical Biochemistry
  • Physiology


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