title: Diffusional effects in the steady state kinetics of ubiquinol cytochrome c reductase in bovine heart submitochondrial particles.
abstract: The steady-state kinetics of ubiquinol cytochrome c reductase was investigated in submitochondrial particles using ubiquinol-1 as electron donor in media of increasing viscosities obtained by water-polyethylene glycol mixtures. The minimum association rate constant, kmin = kcat/km, for cytochrome c was strongly viscosity dependent, whereas kmin for ubiquinol-1 was only weakly affected by viscosity. It is concluded that the interaction of cytochrome c with the membranous reductase is largely under diffusion control, whereas the oxidation of ubiquinol by the enzyme is not significantly controlled by diffusion in either the aqueous medium or the membrane. The results are compatible with the presence of a diffusion limited step in cytochrome c but not in ubiquinone in mitochondrial electron transfer.
authors.affiliation: Department of Biology, University of Bologna, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Fato
authors.forename: C
authors.initials: C
authors.lastname: Castelluccio
authors.forename: S
authors.initials: S
authors.lastname: Armaroli
authors.forename: A
authors.initials: A
authors.lastname: Contarini
authors.forename: G
authors.initials: G
authors.lastname: Parenti Castelli
authors.forename: G
authors.initials: G
authors.lastname: Lenaz
mesh_terms: D000818:Animals; D002417:Cattle; D004058:Diffusion; D014450:Electron Transport Complex III / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008929:Mitochondria, Heart / Q000201:enzymology*; D013367:Submitochondrial Particles / Q000201:enzymology*
chemical_list: D014450:Electron Transport Complex III