Purification and characterization of the rat liver microsomal cytochrome P-450 involved in the 4-hydroxylation of debrisoquine, a prototype for genetic variation in oxidative drug metabolism

Abstract

Genetic polymorphism in oxidative drug metabolism is perhaps best exemplified in the case of debrisoquine 4-hydroxylase activity, where the incidence of deficient metabolism ranges from 1% to 30% in various populations and this defect is also linked to an impaired ability to metabolize a number of other drugs effectively. Sprague-Dawley (SD) rats possess this activity, but females of the DA strain do not, although total cytochrome P-450 (P-450) levels are similar. We have purified, by using debrisoquine 4-hydroxylase activity as an assay, a minor P-450 to electrophoretic homogeneity from male SD rats and designate this as P-450UT-H. P-450UT-H differs from eight other purified rat liver P-450s as judged by peptide mapping and immunochemical analysis and thus appears to be isozymic with these other P-450s. P-450UT-H exhibited considerably more debrisoquine 4-hydroxylase activity than any of the other purified P-450s and, on a total P-450 basis, more than total microsomal P-450. Antibodies raised against P-450UT-H specifically recognized P-450UT-H and inhibited more than 90% of the debrisoquine hydroxylase activity present in SD rat liver microsomes. The level of P-450UT-H in SD rat liver microsomes accounted for less than 10% of the total P-450, as judged by immunochemical quantitation. These assays also indicated that the level of P-450UT-H in female DA rat liver microsomes is only about 5% of that in male or female SD rat liver microsomes, consonant with the view that deficiency of this form of P-450 is responsible for the defective debrisoquine 4-hydroxylase activity in the former animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and reconstitution properties of human placental aromatase. A cytochrome P-450-type monooxygenase

“…Hepatic cytochrome P-450 isozymes purified from rabbits and rats show in the oxidized state absorption coefficients of 84.7 mM-' cm-' at 393 nm [24] and of 131 mM-l cm-' at 417 nm [25], respectively. Compared to these values, the absorption coefficient at 394 nm of our purified aromatase appears low, suggesting only 40 -62% purification, or comigration of inactive enzyme.…”

Extensive oxidative metabolism of dextromethorphan in patients with almitrine neuropathy.

“…Two phenotypes have been identified: most subjects are 'extensive metabolizers', whereas a minority of subjects are 'poor metabolizers' (Mahgoub et al, 1977). The impairment of debrisoquine 4-hydroxylation is inherited as an autosomal recessive trait (Evans et al, 1980) and is related to the deficiency of a particular liver P-450 cytochrome isoenzyme (Larrey et al, 1984;Distelrath et al, 1985). In addition to debrisoquine, this isoenzyme is responsible for the genetic polymorphic oxidation of 30 other drugs, including dextromethorphan and perhexiline maleate (Eichelbaum, 1982;Larrey, 1986 (Eichelbaum, 1982;Larrey, 1986).…”

Polymorphism of dextromethorphan oxidation in a French population.

“…Two phenotypes have been identified: most subjects are 'extensive metabolizers' (EM) whereas a minority of subjects are 'poor metabolizers' (PM) (Mahgoub et al, 1977). The impairment of debrisoquine 4-hydroxylation is inherited as an autosomal recessive trait (Evans etal., 1980) and is related to the deficiency of a particular liver cytochrome P-450 (Larrey et al, 1984;Distlerath et al, 1985). The PM phenotype is found in 3-10% of European and American Caucasians (Kupfer & Preisig, 1983).…”