title: Molecular conversion between monomeric and dimeric states of the mitochondrial cytochrome b-c1 complex: isolation of active monomers.
abstract: Bovine heart cytochrome b-c1 complex dispersed in 0.1% dodecylmaltoside, 10 mM Tris-HCl (pH 7.4), was subjected to filtration on Ultrogel AcA 34 columns. Apparent Mr values of about 400,000 and 170,000 were estimated for the enzyme-detergent complex in the presence and absence of 50 mM KCl, respectively. Similar Mr values (about 390,000 and 160,000) were obtained after sucrose gradient centrifugation of the b-c1 complex species isolated using Ultrogel filtration. Both species contained eight polypeptides, as in the original cytochrome b-c1 complex. The experiments suggest that the two species represent a dimer and a monomer of the b-c1 complex. The molecular conversion between the monomeric and dimeric state of the enzyme was found to be reversible. Both monomers and dimers of the b-c1 complex were competent to catalyze QH2:cytochrome c reductase activity with approximately the same maximal velocity. The finding that both molecular forms of the enzyme appear equally active does not support functional models based exclusively on a dimeric b-c1 complex.
authors.forename: M J
authors.initials: MJ
authors.lastname: Nałecz
authors.forename: R
authors.initials: R
authors.lastname: Bolli
authors.forename: A
authors.initials: A
authors.lastname: Azzi
mesh_terms: D000818:Animals; D002417:Cattle; D002499:Centrifugation, Density Gradient; D055598:Chemical Phenomena; D002621:Chemistry; D002850:Chromatography, Gel; D003902:Detergents; D014450:Electron Transport Complex III; D007700:Kinetics; D046911:Macromolecular Substances; D008929:Mitochondria, Heart / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D011808:Quinone Reductases / Q000378:metabolism*; D013057:Spectrum Analysis
chemical_list: D003902:Detergents; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D009247:NADH, NADPH Oxidoreductases; D011808:Quinone Reductases; D014450:Electron Transport Complex III