Phenytoin 4-hydroxylation by rabbit liver P450IIC3 and identification of orthologs in human liver microsomes.
The ability of rabbit liver microsomes to 4-hydroxylate phenytoin to 5-(4-hydroxyphenyl)-5-phenylhydantoin was studied. No significant difference was observed between the capacity of control and rifampicin, phenobarbital, acetone, 2,3,7,8-tetrachlorodibenzo-p-dioxin and phenytoin induced rabbit liver microsomes to 4-hydroxylate phenytoin. In reconstitution experiments using six purified rabbit cytochromes P450 isozymes, only P450IIC3 was capable of 4-hydroxylating phenytoin whereas P450IA1, P450IA2, P450IIB4, P450IIIA6, and P450IVB1 were inactive. Further, anti-P450IIC3 IgG completely inhibited phenytoin 4-hydroxylase activity in rabbit liver microsomes. The above data suggest a major role for the constitutive isozyme P450IIC3 in phenytoin 4-hydroxylase activity in rabbit liver. In human liver microsomes P450IIC3 IgG inhibited phenytoin 4-hydroxylase activity by 66%, suggesting that an ortholog to rabbit P450IIC3 is in part responsible for this activity in man.
Doecke
C J
CJ
School of Pharmacy, South Australian Institute of Technology, Adelaide.
Sansom
L N
LN
McManus
M E
ME
D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D007158:Immunologic Techniques; D007527:Isoenzymes / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology*; D010672:Phenytoin / Q000378:metabolism*; D011817:Rabbits; D013045:Species Specificity; D013379:Substrate Specificity
D007527:Isoenzymes; D010672:Phenytoin; D003577:Cytochrome P-450 Enzyme System