Measurements of mitochondrial ←H⁺/O quotients: Effects of phosphate and N‐ethylmaleimide

Sidedness of e− Donation and Stoichiometry of H+ Pumps at Sites II + III in Mitochondria from Rat Liver

“…The H+/2e-ratio at site I11 has been reported to be between zero [30,35,36], 2 [9,37-391 and 4 [lo, 12,131. In the present study we find that duroquinol oxidation leads to H ' /2 e-and charge/2 e-ratios close to 8 during operation of site I1 + I11 and H + / 2 e-of 4 and charge/2 e-ratios of 2 during operation of site I1 alone.…”

Compartmentation and Communication in Living Systems. Ligand Conduction: a General Catalytic Principle in Chemical, Osmotic and Chemiosmotic Reaction Systems

“…As seen in Fig.21, the NAD-linked oxidation of P-hydroxybutyrate gave an +H+/O ratio of 6. In similar experiments, the ubiquinone-linked oxidation of succinate and the NADP-linked oxidation of isocitrate gave c H + / O ratios of 4 and 8 respectively [42][43][44][45]49,120,; while, with a somewhat modified technique, the t H ' / 2 e -ratio of the NADP/ NAD transhydrogenase was found to be near 2 [126]. We concluded that in rat liver mitochondria, and in the mitochondrion-like bacterium Paracoccus denitrificans, the t H + / O or c H f / 2 e -ratio per effective redox loop in the respiratory chain is 2.…”

“…The simplest, and I think most reliable, method of measuring t H + / O or t H + / 2 eratios is the 02-pulse or respiratory pulse method [49,, illustrated by Fig. 21.…”

“…23, employing diaminodurene as a specific external reductant reacting with the respiratory chain system at the level of cytochrome c [49]. Added cytochrome c itself was used as reductant in control experiments (Fig.…”

The H+/O stoicheiometry of mitochondrial respiration

“…Mitchell at al. [7,23,25,26] have rejected this claim and proposed that the enhancement of the +H'/2 e-quotient caused by NEM is, in these experiments, due to activation of H' translocating oxidation of endogenous NAD(P)H, rather than to prevention of H' backflow [5,6,8,241. It is agreed that the +-H'/2 e-quotient for electron flow from succinate, or quinol, to cytochrome c3+ is, at neutrality, 4 [7-l 1,17,24]. This, together with the demonstration of an H+/O quotient of 4 for succinate oxidation (or quinol oxidation [IO,1 1,27]), leads to the inescapable conclusion that electron flow at the third site from cytochrome c2+ to oxygen does not cause H+ ejection from mitochondria.…”