Catalytic activity of cytochrome P4501A2 in reconstituted system with Emulgen 913

Physicochemical properties and catalytic activity of cytochrome P4501A2 in the reconstituted system with Emulgen 913 were studied. The formation of cytochrome P4501A2 monomers was shown by gel filtration at an Emulgen concentration of 8 g/liter. The catalytic activity of the monomeric monooxygenase system was low. The maximum rate of the 7-ethoxyresorufin O-deethylation reaction, 150 pmol resorufin min-1 nmol-1 cytochrome P4501A2, was observed at an Emulgen concentration of 0.1 g/liter when cytochrome P4501A2 pentamers predominated. The effects of Emulgen on cytochrome P4501A2 cumene hydroperoxide-dependent peroxidase activity, on its affinity to substrate and to cytochrome b5, and on the rate constants of dithionite-dependent reduction were insignificant. Study of the NADPH-dependent reduction of cytochrome P4501A2 in the reconstituted system showed that the rate constant and reduction level of cytochrome P4501A2 were always higher when the reaction was initiated by NADPH than when it was initiated by NADPH-cytochrome P450 reductase. This indicated that the reduction reaction initiated by the reductase was limited by a step in the cytochrome P4501A2 and reductase interaction. Correlation between 7-ethoxyresorufin O-deethylase activity and reduction level of cytochrome P4501A2 was found.