Differentiation Between Type I and Type II Substrate Binding to Cytochrome P450 by Temperature Studies

Sa？etak The binding reactions of type J and type II substances to cytochrome P450 solubilized from phenobarbital induced rat liver microsomes show different dependence on temperature. With increasing temperature the type II binding is lowered whereas the stability of type I substrate complexes increases. The binding enthalpies were calculated from the van't Hoff plots and discussed in connection with the entropy and Gibbs energy of substrate binding to cytochrome P450. Our data on temperature dependence provide further evidence pointing to a difference between the binding sites of the two classes of substrates, and support the view that the type I binding site is located in a hydrophobic part of the cytochrome P450 molecule