title: [Hysteresis behavior of complex I from bovine heart mitochondria: kinetic and thermodynamic parameters of retarded reverse transition from the inactive to active state].
abstract: Isolated Complex I exists in two forms. The active form catalyzes the rapid rotenone-sensitive, N-ethylmaleimide-insensitive NADH : Q1 reductase reaction. The inactive form is inhibited by N-ethylmaleimide and catalyzes the rotenone-sensitive ubiquinone reduction with a prominent lag phase. The inactive enzyme is transformed into its active form after rapid reduction by NADH and slow (compared with the steady-state turnover number) oxidation by quinone. The rate of activation is strongly temperature-dependent (the activation energy is 170 kJ/mol) and influenced by pH and divalent cations. The active enzyme is quite stable (hours at 0 degrees C) but it is spontaneously deactivated at high temperature (the activation energy is 245 kJ/mol). The active/inactive transition parameters are qualitatively and quantitatively similar for the isolated and membrane-bound Complex I. The extent of the isolated Complex I activation in the presence of NADH depends on the concentration of the added quinone. The concentration of quinone needed for the half-maximal activation is 10 times less than the KQ1m value in the steady-state NADH : Q1 reductase reaction. The data obtained suggest that the free energy of NADH oxidation in the respiratory chain is partly utilized to maintain the catalytically competent Complex I conformation.
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104.
authors.forename: E O
authors.initials: EO
authors.lastname: Maklashina
authors.forename: V D
authors.initials: VD
authors.lastname: Sled'
authors.forename: A D
authors.initials: AD
authors.lastname: Vinogradov
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000494:pharmacology; D002417:Cattle; D004789:Enzyme Activation; D005033:Ethylmaleimide / Q000494:pharmacology; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D012402:Rotenone / Q000494:pharmacology; D013816:Thermodynamics
chemical_list: D016227:Benzoquinones; D012402:Rotenone; C004532:quinone; D016660:NAD(P)H Dehydrogenase (Quinone); D005033:Ethylmaleimide
vernacular_title: Gisterezisnoe povedenie kompleksa I mitokhondriĭ serdtsa byka: kineticheskie i termodinamicheskie parametry medlennogo obratimogo perekhoda iz neaktivnogo v aktivnoe sostoianie.