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. Involved in ergosterol biosynthesis. Has NADPH-dependent ferrireductase activity on the plasma membrane. NADPH + 2 oxidized [cytochrome P450] = H(+) + NADP(+) + 2 reduced [cytochrome P450] Binds 1 FAD per monomer. Binds 1 FMN per monomer. The Vmax of the reaction is 721 pmol/min/pmol enzyme towards cytochrome c, and 662 pmol/min/pmol enzyme toward NADPH. Interacts with PCL1. By galactose and on the plasma membrane by iron or copper deficiency. Repressed by glucose. Phosphorylated by the cyclin-CDK PCL1-PHO85. Accumulates 20% of ergosterol of wild type. Present with 46600 molecules/cell in log phase SD medium. Belongs to the NADPH--cytochrome P450 reductase family. In the N-terminal section; belongs to the flavodoxin family. In the C-terminal section; belongs to the flavoprotein pyridine nucleotide cytochrome reductase family.