Identification of residues 286 and 289 as critical for conferring substrate specificity of human CYP2C9 for diclofenac and ibuprofen

Arch Biochem Biophys. 1998 Sep 15;357(2):240-8. doi: 10.1006/abbi.1998.0826.


Specificity of human CYP2C9 for two substrates, diclofenac and ibuprofen, was studied using chimeras and site-directed mutants of CYP2C9 and the highly related CYP2C19 expressed in Escherichia coli. Data were correlated with the presence of putative substrate recognition sites (SRS). A CYP2C19 chimera containing residues 228-340 (SRS 3 and 4) of 2C9 conferred both diclofenac hydroxylation and 2- and 3-hydroxylation of ibuprofen. The regiospecificity of this construct for metabolism of ibuprofen differed from that of CYP2C9 by favoring 2-hydroxylation over 3-hydroxylation. A CYP2C9 construct containing residues 228-340 of CYP2C19 lacked both diclofenac and ibuprofen hydroxylase activities. When residues 228-282 (containing SRS 3) of CYP2C9 were replaced by those of CYP2C19, the chimera retained appreciable activity for diclofenac and ibuprofen, and tolbutamide activity was inhibited by a specific CYP2C9 inhibitor, sulfaphenazole. This suggested that SRS 3 is not important in conferring specificity. CYP2C9 and CYP2C19 differ in five residues within the region 283-340 (within SRS 4). Mutations to analyze SRS 4 were made on a CYP2C19 chimera containing residues 228-282 of CYP2C9. A single I289N mutation conferred a dramatic increase in diclofenac hydroxylation and a small increase in ibuprofen 2-hydroxylation. A second mutation (N286S and I289N) increased diclofenac hydroxylation and conferred a dramatic increase in ibuprofen 2-hydroxylation. A V288E mutation did not increase activity toward either substrate and decreased activity toward the two substrates in combination with the I289N or the N286S, I289N mutants. Therefore residues 286 and 289 of CYP2C9 are important in conferring specificity for diclofenac and ibuprofen.

MeSH terms

  • Aryl Hydrocarbon Hydroxylases*
  • Cytochrome P-450 CYP2C19
  • Cytochrome P-450 CYP2C9
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism*
  • Diclofenac / metabolism*
  • Enzyme Activation / drug effects
  • Enzyme Activation / genetics
  • Escherichia coli / genetics
  • Humans
  • Hydroxylation
  • Ibuprofen / metabolism*
  • Mixed Function Oxygenases / genetics
  • Mutagenesis, Site-Directed
  • Protein Binding / drug effects
  • Protein Binding / genetics
  • Recombinant Fusion Proteins / genetics
  • Steroid 16-alpha-Hydroxylase*
  • Steroid Hydroxylases / antagonists & inhibitors
  • Steroid Hydroxylases / genetics
  • Steroid Hydroxylases / metabolism*
  • Substrate Specificity / genetics
  • Tolbutamide / metabolism


  • Cytochrome P-450 Enzyme Inhibitors
  • Recombinant Fusion Proteins
  • Diclofenac
  • Cytochrome P-450 Enzyme System
  • Tolbutamide
  • Mixed Function Oxygenases
  • Steroid Hydroxylases
  • CYP2C9 protein, human
  • Cytochrome P-450 CYP2C9
  • Aryl Hydrocarbon Hydroxylases
  • CYP2C19 protein, human
  • Cytochrome P-450 CYP2C19
  • Steroid 16-alpha-Hydroxylase
  • Ibuprofen