USE OF SELECTIVE CHEMICAL MODIFICATION OF CYTOCHROME P450SCC (CYPXIA1) WITH FLUORESCEIN ISOTHIOCYANATE TO EVALUATE INTRAMOLECULAR DISTANCESAND CONFORMATIONAL-CHANGES BY RESONANT FLUORESCENCE ENERGY-TRANSFER

Chemical modification of cytochrome P450scc with fluorescein isothiocy anate (FITC) selectively adds the fluorescent label to Lys(338). Using affinity chromatography on immobilized adrenodoxin, it was shown that the cytochrome P450scc containing the fluorescent group retains the a bility to physically interact with ferredoxin. Fluorescent labelling d oes not affect the enzymatic activity of the hemoprotein at the step o f the first electron transfer. Based on the intramolecular resonant en ergy transfer efficiency within the donor-acceptor pair (FITC-heme), t he distance between the heme group and Lys(338) of the cytochrome P450 scc molecule was calculated to be 2.81 nm. Changes in this distance up on the transition of cytochrome P450scc from oligomeric to monomeric a nd high-spin to low-spin forms, as well as conversion into cytochrome P420 by thermal or alkaline treatment or complete denaturation of the protein globule in 6 M guanidine hydrochloride, were demonstrated. It is concluded that the selective chemical modification of cytochrome P4 50scc with FITC is an informative method which can be used to monitor conformational changes in the cytochrome P450scc molecule during the p rocess of monooxygenation.