This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes. It can also provide electron transfer to heme oxygenase and cytochrome B5. NADPH + 2 oxidized [cytochrome P450] = H(+) + NADP(+) + 2 reduced [cytochrome P450] Binds 1 FAD per monomer. Binds 1 FMN per monomer. Belongs to the NADPH--cytochrome P450 reductase family. In the C-terminal section; belongs to the flavoprotein pyridine nucleotide cytochrome reductase family. In the N-terminal section; belongs to the flavodoxin family.