The absorbance spectra of SbCPR2s and anaerobic titration of CPR proteins with NADPH.A, exemplifies a series of spectra obtained with SbCPR2s and rat CPR. The spectra shown correspond to NADPH:CPR ratios of 0, 0.5, 1, 2, 4, and 16. B, the changes in absorbance at 456 and 595 nm. CPR concentrations were normalized to 1 mM prior to plotting. CPR, cytochrome P450 reductase.