Nitric oxide synthase reductase domain (NOS reductase domain)

The Nitric Oxide Synthase (NOS) reductase domain is the C-terminal portion of the NOS enzyme, responsible for supplying electrons required for the conversion of L-arginine to nitric oxide (NO). It contains binding sites for flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), and nicotinamide adenine dinucleotide phosphate (NADPH), showing high homology to cytochrome P450 reductase (UniProt). This domain is historically referred to as the diaphorase domain due to its ability to reduce exogenous electron acceptors like nitroblue tetrazolium in histochemical assays (PubMed). In the presence of calcium and calmodulin, the reductase domain undergoes a conformational change that allows electron transfer to the N-terminal oxygenase domain's heme center (PubMed). Dysregulation of this electron transfer process is linked to various pathologies, including cardiovascular diseases like hypertension and atherosclerosis, as well as neurodegenerative conditions and inflammatory disorders (NIH). While most therapeutic inhibitors target the oxygenase domain's arginine-binding site, the reductase domain and its interaction with calmodulin represent critical regulatory checkpoints for modulating NO production. Pharmacological modulation of this domain, such as through flavoprotein inhibitors or calmodulin antagonists, provides a mechanism to control NO levels in disease states like septic shock or chronic pain.

Other names

NADPH-diaphoraseNOS C-terminal domainNitric oxide synthase diaphorase domainNOS flavoprotein domain

Catalyzes the transfer of electrons from NADPH through FAD and FMN to the heme center in the oxygenase domain, a process strictly regulated by calmodulin binding.