title: Mechanism of rate control of the NADPH-dependent reduction of cytochrome P-450 by lipids in reconstituted phospholipid vesicles.
abstract: The NADPH-supported reduction of cytochrome P-450 LM2 (liver microsomal isozyme 2) in reconstituted phospholipid vesicles in general exhibits two-exponential kinetics. The physiologically relevant rapid partial reaction is favoured in amount with increasing reductase/P-450 ratio. A lipid specificity was observed in that negatively charged lipids favour that process, too. The rate constant increases concomitantly. The data are consistent with the formation of a reactive 1:1 complex the amount of which determines the rate constant. The dissociation constants amount to 0.048 microM for a microsomal lipid extract, 0.051 microM for a 3:1 (w/w) mixture of dioleoylglycerophosphoethanolamine and phosphatidylserine, and 0.47 microM for dioleoylglycerophosphocholine, respectively, in the respective reconstituted systems. At low reductase/P-450 ratio the amount of the rapidly reduced P-450 exceeds the equilibrium concentration of a 1:1 complex. Preformed 1:1 associates, therefore, cannot fit the derived mechanism. Instead, a cluster model based on P-450 association does correspond to the data.
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D050356:Lipid Metabolism; D008433:Mathematics; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D010743:Phospholipids; D009249:NADP; D003577:Cytochrome P-450 Enzyme System