On the 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.