Studies on the association of cytochrome P-450 and NADPH-cytochrome c reductase during catalysis in a reconstituted hydroxylating system.
The interaction between cytochrome P-450 and NADPH-cytochrome c reductase during catalysis has been investigated with a reconstituted monooxygenase system composed of the two purified enzyme components and synthetic phospholipid. Steady state kinetic data are consistent with a scheme in which the formation of a binary complex between the two proteins precedes catalysis. The formation of this binary complex is described by a simple mass action equation. In agreement with this equation, the observed Vmax for benzphetamine N-demethylation was found to be directly proportional to the calculated concentration of the cytochrome P-450 . reductase complex. Furthermore, with appropriate reductase/cytochrome P-450 mole ratios, the Vmax could be shown to be linearly dependent on either the reductase or the cytochrome P-450 concentration alone. In contrast, the Km parameter is independent of the complex concentration, indicating that no change in the rate-limiting step has occurred. Thus a distinction should be made between a rate-limiting enzyme component and the rate-limiting step in this multienzyme system.
D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003579:Cytochrome Reductases / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism*; D010105:Oxygenases / Q000378:metabolism; D010634:Phenobarbital / Q000494:pharmacology; D010743:Phospholipids / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats
D046911:Macromolecular Substances; D010743:Phospholipids; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; D003579:Cytochrome Reductases; D009251:NADPH-Ferrihemoprotein Reductase; D010634:Phenobarbital