TY - JOUR T1 - CYP2C9 - CYP3A4 Protein-Protein Interactions: Role of the Hydrophobic N-Terminus JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.109.030155 SP - dmd.109.030155 AU - Murali Subramanian AU - Harrison Tam AU - Helen Zheng AU - Timothy S. Tracy Y1 - 2010/03/09 UR - http://dmd.aspetjournals.org/content/early/2010/03/09/dmd.109.030155.abstract N2 - Cytochrome P450s interact with redox transfer proteins, including cytochrome P450 reductase (CPR) and cytochrome b5 (b5), all being membrane bound. In multiple in-vitro systems, P450-P450 interactions also have been observed resulting in alterations in enzymatic activity. The current work investigated the effects and mechanisms of interaction between CYP2C9 and CYP3A4 in a reconstituted system. CYP2C9-mediated metabolism of S-naproxen and S-flurbiprofen were inhibited up to 80% by co-incubation with CYP3A4, although Km values were unchanged. Increasing CYP3A4 concentrations increased the degree of inhibition, whereas increasing CPR concentrations resulted in less inhibition. Addition of b5 only marginally affected the magnitude of inhibition. In contrast, CYP2C9 did not alter the CYP3A4-mediated metabolism of testosterone and midazolam. The potential role of the hydrophobic N-terminus on these interactions, was assessed by incubating truncated CYP2C9 with full length CYP3A4, and vice-versa. In both instances, the inhibition was fully abolished indicating an important role for hydrophobic forces in CYP2C9-CYP3A4 interactions. Finally, a CYP2C9:CYP3A4 heteromer complex was isolated by co-immunoprecipitation techniques, confirming the physical interaction of the proteins. These results demonstrate that the N-terminus membrane binding domains of CYP2C9 and CYP3A4 are involved in heteromer complex formation and that at least one consequence is a reduction in CYP2C9 activity.The American Society for Pharmacology and Experimental Therapeutics ER -