[Reduction of cytochrome P-450 by methylviologen free radicals]

Kinetics of cytochrome P-450 reduction with methylviologen radicals was investigated by flash-photolysis. Formation of carboxycomplex of reduced protein and effect of temperature and substrates of the I type on this reaction were studied. It has been shown that CO addition to protein proceeds in two stages. With temperature increase (20-45 degrees C) and when benzphetamine or hexabarbital are added to solution the weight of the first (faster) stage increases. Such regularity is easily explained by the presence in solution of two conformers of oxidized cytochrome P-450 (with different reactivity) whose equilibrium depends on temperature and presence of the substrate.