title: [Use of spin-labelled substrate analogs for a comparative study of microsomal cytochrome P-450 and P-448].
abstract: The previously described, iodine-labeled alkylating stable nitroxyl radicals located at different distances between the N-O. group and the iodine atom were used for a comparative study of the structure of microsomal cytochromes P-450 and P-448 active centers. The radicals were shown to change the optical spectra of Fe3+ located in the active site of the enzyme that are similar to those induced by cytochrome P-450 substrates. Some differences in the type of the radicals binding to control, phenobarbital- and 3-methylcholanthrene-induced microsomes were revealed. The alkylating radical substrate analogs covalently bound to microsomal cytochrome P-450 in the vicinity of the active center, resulting in the inhibition of oxidation of type I and II substrates (e. g., aniline and naphthalene). The value of the spectral binding constant (Ks) for naphthalene in the presence of the radical covalently bound to the cytochrome P-450 active center showed a tendency to increase. Using the ESR technique, the interaction between Fe3+ and the radical localized in the active site of cytochrome P-450 was demonstrated. The contribution of Fe3+ to the relaxation of the radicals covalently bound to cytochrome P-450 was evaluated from the values of the spin label ESR spectra saturation curves at 77K. The distances between the N-O. group of these radicals and Fe3+ in the enzyme active center for the three types of microsomes were determined. The data obtained point to structural peculiarities of the active center of cytochrome P-450, depending on the microsomal type.
authors.forename: V I
authors.initials: VI
authors.lastname: Popova
authors.forename: L M
authors.initials: LM
authors.lastname: Vaĭner
authors.forename: I I
authors.initials: II
authors.lastname: Gorshkova
authors.forename: O A
authors.initials: OA
authors.lastname: Gromova
authors.forename: V V
authors.initials: VV
authors.lastname: Liakhovich
mesh_terms: D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D019388:Cytochrome P-450 CYP1A2; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009281:Naphthalenes / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013113:Spin Labels
chemical_list: D000814:Aniline Compounds; D003580:Cytochromes; D009281:Naphthalenes; D013113:Spin Labels; D003577:Cytochrome P-450 Enzyme System; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; C023650:aniline
vernacular_title: Ispol'zovanie spin-mechenykh analogov substratov dlia sravnitel'nogo izucheniia mikrosomal'nykh tsitokhromov P-450 i P-448.