Abstract
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.
Original language | English |
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Pages (from-to) | 1112-1118 |
Number of pages | 7 |
Journal | Biochemical and Biophysical Research Communications |
Volume | 175 |
Issue number | 3 |
DOIs | |
Publication status | Published - 29 Mar 1991 |
Keywords
- human liver
- isozymes
- tolbutamide