title: [Interactions of microsomal cytochrome P-450 with spin-labeled substrate analogs].
abstract: The iodine-containing stable iminoxyl radicals with various distances between the N-O-group and the iodine atom are proposed to be used to study the structure of the active center of the microsomal cytochrome P-450. The radicals used induce changes in the optical spectra of the Fe3+ ion located in the active center of the enzyme, as in the case of type 1 substrates and inhibit essentially the microsomal oxidation of cytochrome P-450 substrates of type 1 and 2. This inhibition is neither due to suppression of the NADPH-cytochrome c reductase activity nor to cytochrome P-450 conversion to cytochrome P-420. Cytochrome P-450 substrates (aminopyrine) protect the enzyme against the radical-induced inactivation. The iodine-containing radicals are covalently bound to cytochrome P-450 in the vicinity of active center. The values of dissociation constants for the reversible enzyme-radical constants and the rate constants for the monomolecular transformation in the complex, k, were determined. The EPR method was used to detect the coupling between Fe3+ and the radical located in the active center of cytochrome P-450. The saturation curves of radical SPR spectra at 77 degrees K were employed to determine the contribution of Fe3+ to the relaxation time, T1, of the radicals covalently bound to cytochrome P-450 and to estimate the distances between the Fe3+ ion and the N-O-group of these radicals in the enzyme active center.
mesh_terms: D000818:Animals; D001665:Binding Sites; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007700:Kinetics; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013113:Spin Labels / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D005609:Free Radicals; D013113:Spin Labels; D003577:Cytochrome P-450 Enzyme System
vernacular_title: Vzaimodeĭstvie mikrosomal'nogo tsitokhroma P-450 so spin-mechenymi analogami substratov.