title: Cytochrome P-450 2E1 is not the sole catalyst of chlorzoxazone hydroxylation in rat liver microsomes. off.
abstract: The contribution of individual cytochrome P-450 isozymes in the hydroxylation of the centrally acting skeletal muscle relaxant chlorzoxazone was determined in rat liver microsomes. The hydroxylation rate of chlorzoxazone was found to be 50% greater in male than female microsomes. Kinetic studies using control male microsomes showed that chlorzoxazone hydroxylation was biphasic with a calculated low Km (33 microM) and high Km (116 microM). Liver microsomes from isoniazid-, beta-naphthoflavone- or dexamethasone-treated male rats produced a Km of 93, 69 and 26 microM, respectively. When chlorzoxazone hydroxylation activity was measured at a high substrate concentration (200 microM), treatment of male rats with isoniazid, acetone, beta-naphthoflavone and dexamethasone produced increases in the activity rate of 124%, 117%, 81% and 32%, respectively. However, when the activity was measured at a low substrate concentration (2 microM), liver microsomes from dexamethasone-treated male and female rats produced 5- and 10-fold induction, respectively. In immunoinhibition studies at 200 microM of chlorzoxazone, antibodies specific for cytochrome P-450 2E1 inhibited the rate of chlorzoxazone hydroxylation in microsomes from control and isoniazid-treated male rats by 68% and 79%, respectively. A monoclonal antibody (C8) against P-450 1A1 inhibited 67% of the activity in microsomes from beta-naphthoflavone-treated male rats but was ineffective inhibiting chlorzoxazone hydroxylation in microsomes from control or dexamethasone-treated male rats. In liver from control female rats, antibodies against cytochrome P-450 2E1 inhibited 80% of chlorzoxazone hydroxylation, whereas it inhibited only 47% of the activity in dexamethasone-treated females.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Rhône-Poulenc Rorer Central Research, Drug Safety Division, Cóllegeville, Pennsylvania, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Jayyosi
authors.forename: D
authors.initials: D
authors.lastname: Knoble
authors.forename: M
authors.initials: M
authors.lastname: Muc
authors.forename: J
authors.initials: J
authors.lastname: Erick
authors.forename: P E
authors.initials: PE
authors.lastname: Thomas
authors.forename: M
authors.initials: M
authors.lastname: Kelley
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D002384:Catalysis; D002753:Chlorzoxazone / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D019392:Cytochrome P-450 CYP2E1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005260:Female; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000911:Antibodies, Monoclonal; D003577:Cytochrome P-450 Enzyme System; D019392:Cytochrome P-450 CYP2E1; D010089:Oxidoreductases, N-Demethylating; D002753:Chlorzoxazone