title: Catalytic activity of cytochromes c and c1 in mitochondria and submitochondrial particles.
abstract: 1. Beef heart mitochondria have a cytochrome c1:c:aa3 ratio of 0.65:1.0:1.0 as isolated; Keilin-Hartree submitochondrial particles ahve a ratio of 0.65:0.4:1.0. More than 50% of the submitochondrial particle membrane is in the 'inverted' configuration, shielding the catalytically active cytochrome c. The 'endogenous' cytochrome c of particles turns over at a maximal rate between 450 and 550 s-1 during the oxidation of succinate or ascorbate plus TMPD; the maximal turnover rate for cytochrome c in mitochondria is 300-400 s-1, at 28 degrees-30 degrees C, pH 7.4. 2. Ascorbate plus N,N,N',N'-tetramethyl-p-phenylene diamine added to antimycin-treated particles induces anomalous absorption increases between 555 and 565 nm during the aerobic steady state, which disappear upon anaerobiosis; succinate addition abolishes this cycle and permits the partial resolution of cytochrome c1 and cytochrome c steady states at 552.5-547 nm and 550-556.5 nm, respectively. 3. Cytochrome c1 is rather more reduced than cytochrome c during the oxidation of succinate and of ascorbate + N,N,N',N'-tetramethyl-p-phenylene diamine in both mitochondria and submitochondrial particles; a near equilibrium condition exists between cytochromes c1 and c in the aerobic steady state, with a rate constant for the c1 leads to c reduction step greater than 10(3) s-1. 4. The greater apparent response of the c/aa3 electron transfer step to salts, the hyperbolic inhibition of succinate oxidation by azide and cyanide, and the kinetic behaviour of the succinate-cytochrome c reductase system, are all explicable in terms of a near-equilibrium condition prevailing at the c1/c step. Endogenous cytochrome c of mitochondria and submitochondrial particles is apparently largely bound to cytochrome aa3 units in situ. Cytochrome c1 can either reduce the cytochrome c-cytochrome aa3 complex directly, or requires only a small extra amount of cytochrome c to carry the full electron transfer flux.
mesh_terms: D000332:Aerobiosis; D000818:Animals; D001386:Azides / Q000494:pharmacology; D002417:Cattle; D003486:Cyanides / Q000494:pharmacology; D003574:Cytochrome c Group / Q000031:analogs & derivatives* / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism; D003575:Cytochromes c1 / Q000378:metabolism*; D004579:Electron Transport; D007700:Kinetics; D008433:Mathematics; D008566:Membranes / Q000378:metabolism; D008931:Mitochondria, Muscle / Q000187:drug effects / Q000378:metabolism*; D009206:Myocardium; D051381:Rats; D013053:Spectrophotometry
chemical_list: D001386:Azides; D003486:Cyanides; D003574:Cytochrome c Group; D003580:Cytochromes; D003575:Cytochromes c1