Redox sensor protein. Undergoes restructuring and subcellular redistribution in response to changes in intracellular NADPH/NADP(+) levels. At low NADPH concentrations the protein is found mainly as a monomer, and binds argininosuccinate synthase (ASS1), the enzyme involved in nitric oxide synthesis. Association with ASS1 impairs its activity and reduces the production of nitric oxide, which subsecuently prevents apoptosis. Under normal NADPH concentrations, the protein is found as a dimer and hides the binding site for ASS1. The homodimer binds one molecule of NADPH. Has higher affinity for NADPH than for NADP(+). Binding to NADPH is necessary to form a stable dimer. Homodimer. Interacts with ASS1. Interaction is enhanced by low NADPH/NADP(+) ratios, which results in inhibition of ASS1 activity. Under normal redox growth conditions localizes in the cytoplasm and perinuclear region. Nuclear localization is promoted by increased intracellular nitric oxide and reduced NADPH/NADP(+) ratios. By nitric oxide, cGMP and pro-inflammatory cytokines. Reduced levels of NMRAL1 by RNAi increases nitric oxide production and reduces cell viability. Overexpression of NMRAL1 increases cell viability. 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.