The K+/site and H+/site stoichiometry of mitochondrial electron transport.
Electrode measurements of the average number of H+ ejected and K+ taken up (in the presence of valinomycin) per pair of electrons passing the energy-conserving sites of the respiratory chain of rat liver and rat heart mitochondria have given identical values of the H+/site and 5+/site ratios very close to 4 in the presence of N-ethylmaleimide, an inhibitor of interfering respiration-coupled uptake of H+ + H2PO4-. The K+/site uptake ratio of 4 not only shows that inward movement of K+ provides quantitative charge-compensation for the 4 H+ ejected, but also confirms that 4 charges are separated per pair of electrons per site. When N-ethylmaleimide is omitted, the H+/site ejection ratio is depressed, because of the interfering secondary uptake of H/+ with H2PO4- on the phosphate carrier, but the K+/site uptake ratio remains at 4.0. Addition of phosphate or acetate, which can carry H+ into respiring mitochondria, further depresses the H+/site ratio, but does not affect the K+/site ratio, which remains at 4.0. These and other considerations thus confirm our earlier stoichiometric measurements that the average H+/site ratio is 4.0 and also show that the K+/site uptake ratio can be used as a measure of the intrinsic H+/site ratio, regardless of the presence of phosphate in the medium and without the necessity of adding N-ethylmaleimide or other inhibitors of H+ + H2PO4- transport.
D000818:Animals; D004579:Electron Transport / Q000187:drug effects; D005033:Ethylmaleimide / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D010101:Oxygen Consumption; D011188:Potassium / Q000378:metabolism*; D011773:Pyruvates / Q000378:metabolism; D051381:Rats
D008293:Malates; D011773:Pyruvates; D009243:NAD; D006859:Hydrogen; D005033:Ethylmaleimide; D011188:Potassium