title: Proton translocation coupled to quinone reduction by reduced nicotinamide--adenine dinucleotide in rat liver and ox heart mitochondria.
abstract: Measurements were made of the stoicheiometry of proton-translocation coupled to NAD(P)H oxidation by several quinones (duroquinone, ubiquinone(0), ubiquinone(1), ubiquinone(2)) in mitochondria from rat liver and ox heart. Observed stoicheiometries of protons translocated per mol of NADH oxidized (-->H(+)/2e(-) ratios; Mitchell, 1966) ranged from 0.75 (rat liver mitochondria with ubiquinone(1)) to 1.55 (ox heart mitochondria with ubiquinone(1) or ubiquinone(2)). Only the rotenone-sensitive pathway of NADH oxidation by quinone was able to support proton translocation. Correction of the observed -->H(+)/2e(-) ratios for the loss of reducing equivalents to the rotenone-insensitive pathway increased their value to approx. 2.0. It is concluded that the rotenone-sensitive NADH- ubiquinone reductase activity of the respiratory chain may be organized in the mitochondrial membrane as a proton-translocating oxidoreduction loop. The number of such loops between NADH and ubiquinone is one, and not two, as initially proposed by Mitchell (1966).
mesh_terms: D000818:Animals; D002417:Cattle; D005470:Fluorometry; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008566:Membranes; D008928:Mitochondria / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D011048:Polarography; D011522:Protons; D011809:Quinones / Q000378:metabolism*; D051381:Rats; D012402:Rotenone / Q000494:pharmacology; D013056:Spectrophotometry, Ultraviolet; D013386:Succinates; D014451:Ubiquinone / Q000378:metabolism
chemical_list: D011522:Protons; D011809:Quinones; D013386:Succinates; D012402:Rotenone; D009243:NAD; D014451:Ubiquinone; D009249:NADP; D006859:Hydrogen