[Interaction of substrate with cytochrome P-450 in microsomal and solubilized form]

In order to characterize the substrate binding sites, difference spectroscopic titrations in microsomal and solubilized cytochrome P-450 from induced and non-induced rat liver microsomes were performed. The binding constants determined show differences depending on the physicochemical nature of the substrate and the degree of integration of the enzyme system. In hydrophilic substrates the differences of the binding to the microsomal or solubilized form are less pronounced than in lipophilic ones. From the comparison of the parameters obtained at various levels of integration it is concluded that the micromilieu of the binding site is of great importance for the binding of the substrate of cytochrome P-450.