Redox sensor protein. Undergoes restructuring and subcellular redistribution in response to changes in intracellular NADPH/NADP(+) levels (By similarity). Homodimer. Belongs to the NmrA-type oxidoreductase family. Lacks the conserved Tyr residue in the active site triad of Ser-Tyr-Lys necessary for dehydrogenase activity, suggesting that it has no oxidoreductase activity.