rCPR was also evaluated as an alternative to hCPR in the CYP2C9-CYP3A4 interaction experiments, and essentially similar inhibition was noted (Table 1). For cost and availability reasons, rCPR was used in all the subsequent activity experiments involving flurbiprofen as a substrate. The effect of b5 on the CYP2C9-CYP3A4 interactions was examined because the presence of the redox protein b5 can increase P450 metabolism rates for certain substrates and enzymes, particularly CYP3A4. In addition, b5 can also bind to both proteins, hence potentially affecting the CYP2C9-CYP3A4. Figure 3 depicts CYP2C9-mediated metabolism of flurbiprofen in the presence of b5, CPR, and CYP3A4, and the percentage inhibition data from these experiments are presented in Table 1. It is noteworthy that b5 only marginally affected the amount of inhibition of CYP2C9 activity.