Cytochrome P-450 rotamers control mixed-function oxygenation in reconstituted membranes. Rotational diffusion studied by delayed fluorescence depolarization^d`

Abstract

1. Rotational diffusion of purified rabbit-liver microsomal cytochrome P-450 LM₂ in reconstituted lipid-vesicle membranes was investigated by measurement of timedependent polarized emission of delayed fluorescence.

2. Cytochrome P-450 labelled with diiodofluorescein iodoacetamide exhibited strict uniaxial rotation about the normal to the membrane.

3. Benzphetamine retards rotation, while reduction of the cytochrome P-450 substratecomplex accelerates rotation.

4. A model is proposed in which cytochrome P-450 forms disc-shaped rotamers immersed in the bilayer membrane to a depth which is varied by substrate-induced and redox state-dependent conformational changes. The model describes a regulating mechanism of the electron transfer-controlling mixed-function oxygenation.