A constitutive form of guinea pig liver cytochrome P450 closely related to phenobarbital inducible P450b(e).
In order to provide evidence that a cytochrome P450 belonging to the IIB subfamily is expressed as a constitutive form in the guinea pig, we tried to purify an isozyme from liver microsomes of untreated guinea pigs by assessing its reactivity with anti-P450b antibody in the present study. One form of cytochrome P450, named P450GP-1, was obtained. The minimum molecular weight of this isozyme was estimated to be 52,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amino terminal sequence up to the 33rd amino acid of P450GP-1 was determined. As expected, comparison of the amino acid sequence with those of cytochrome P450 isozymes from other species reported so far indicated that P450GP-1 was highly homologous to P450s categorized in the IIB subfamily; that is, 67% similarity to rat P450b, 82% to rabbit LM2, 76% to dog PBD-2, 70% to mouse pf 3/46, and 73% to human IIB1. On the other hand, P450GP-1 showed only low similarity, less than 41%, to other cytochrome P450s of the II subfamily and those of the I, III, and IV families. Affinity of P450GP-1 to anti-P450b immunoglobulin G was confirmed to be comparable with that of a principal antigen, P450b. Immunoblot analysis revealed that P450GP-1 in the guinea pig liver microsomes was induced by phenobarbital treatment, but the increase was not as large as in the rat. P450GP-1 efficiently catalyzed benzphetamine N-demethylation, strychnine 2-hydroxylation, and testosterone 16 beta-hydroxylation, all of which are also catalyzed by P450b. Based on these results, it was strongly suggested that the IIB-type of cytochrome P450 in guinea pigs, at least one of them, is a constitutive form which is moderately induced by phenobarbital.
Oguri
K
K
Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Kaneko
H
H
Tanimoto
Y
Y
Yamada
H
H
Yoshimura
H
H
D000595:Amino Acid Sequence; D000818:Animals; D003429:Cross Reactions; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004790:Enzyme Induction; D006168:Guinea Pigs; D006801:Humans; D015151:Immunoblotting; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D010634:Phenobarbital / Q000494:pharmacology; D012689:Sequence Homology, Nucleic Acid; D013331:Strychnine / Q000378:metabolism
D003577:Cytochrome P-450 Enzyme System; D013331:Strychnine; D010634:Phenobarbital