ON PROBLEM OF POSSIBLE OTHER FORMS OF CYTOCHROME P450 IN LIVER MICROSOMES

The absolute spectrum of cytochrome P450 is shown. The addition of a known substrate is shown to alter the absolute spectrum of this hemoprotein. The spectrum of P450 induced by polycyclic hydrocarbons appeared similar to that of the hemoprotein in the presence of substrate. This similarity is shown to be due to the binding of the inducer and/or its metabolites to the hemoprotein by the ability to displace them and restore the absolute spectrum to that of the native hemoprotein. This study indicates that P450 exists in only two forms, the native enzyme and the enzyme-substrate complex in prepared microsomes. © 1969.