Interaction of Steroid Substrates with Cytochrome P-450C21-Proteoliposomes
Interaction of steroid substrates with P-450C21 incorporated into the single bilayer phosphatidylcholine liposomes was studied in the equilibrium state by measuring substrate-induced spectral change. The apparent dissociation constant of the P-450C21-substrate complex increased with PC concentration in the system, showing the substrate to be partitioned between the aqueous and lipid phases. Using a stopped flow method, the binding kinetics of the substrates to P-450c21 in the liposomes and their dissociation were analyzed at a rapid equilibrium of partitioning. Based on these kinetic analysis, the substrate binding site of P-450C21 was concluded to face the lipid phase of the liposome membranes.
KeywordsLipid Phase Substrate Binding Site Liposome Membrane Dissociation Rate Constant Rapid Equilibrium
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