Fig. 5.

CPR cannot reduce ritonavir-bound CYP3A4. Spectra were recorded under anaerobic conditions in buffer A before (___) and after addition of NADPH and catalytic amounts of human CPR to ligand-free (A), androstenedione- (B), or ritonavir-bound CYP3A4 (C) in the absence (- - - -) or presence of CO (…).