Interaction of microsomal cytochrome P-450 with spin-labelled substrates

Abstract

Iminoxyle derivatives bearing N-alkyl groups were used to study the microsomal hydroxylating system of rat liver. The extent of spin-labelled substrate binding to microsomes, the intensity of substrate-induced spectral changes of cytochrome P-450 and the microsomal hydroxylating activity were used to study the direct binding of spin-labelled substrates (SLS) to cytochrome P-450. Spin-labelled substrates bound to cytochrome P-450 were immobilized and had no contact with the aqueous phase. Sodium desoxycholate, urea and, to a lesser extent, para-chlormercuribenzoate ( p-CMB), increased the molecular mobility of bound spin-labelled substrates. A possible mechanism for cytochrome P-450 interaction with substrates is discussed.