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. Reduces a variety of substrates in vitro, such as cytochrome c, feericyanide and dichloroindophenol. NADPH + 2 oxidized [cytochrome P450] = H(+) + NADP(+) + 2 reduced [cytochrome P450] Binds 1 FAD per monomer. Binds 1 FMN per monomer. A number of isoforms are produced. According to EST sequences. Expressed in roots, leaves, stems, flowers and siliques. Saccharomyces cerevisiae expressing Glycyrrhiza uralensis CYP88D6 and CYP72A154, combined with the expression of Arabidopsis thaliana beta-amyrin synthase (beta-AS) and NADPH-cytochrome P450 reductase 1 (ATR1), accumulates glycyrrhetinic acid (GA) and, to lower levels, beta-amyrin; these GA production was increased in the presence of G.uralensis cytochrome b5 (CYB5). 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.