A human cytochrome P4502C9 cDNA clone has been isolated from a human liver bacteriophage Lambda gt11 library using oligonucleotide probes. Expression of the 1762 base pair cDNA in COS cells demonstrated that the encoded enzyme has a molecular mass of 55 kDa as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The expressed enzyme catalysed the methylhydroxylation of tolbutamide with an apparent Km of 131.7 μM, similar to that observed in human liver microsomes. P4502C9 also catalysed the 4-hydroxylation of phenytoin, and inhibition experiments demonstrated that phenytoin was a competitive inhibitor of tolbutamide hydroxylation with an apparent Ki of 19.1 μM. Sulphaphenazole was a potent inhibitor of the expressed enzyme with respect to both tolbutamide and phenytoin hydroxylations. These data demonstrate that a single isozyme can catalyse the hydroxylations of both tolbutamide and phenytoin, and suggest that both reactions are mediated by the same isozyme(s) of cytochrome P450 in human liver.
|Number of pages||7|
|Journal||Biochemical and Biophysical Research Communications|
|Publication status||Published - 29 Mar 1991|
- human liver