Produces nitric oxide (NO) which is a messenger molecule with diverse functions throughout the body. In the brain and peripheral nervous system, NO displays many properties of a neurotransmitter. Probably has nitrosylase activity and mediates cysteine S-nitrosylation of cytoplasmic target proteins such SRR. Isoform NNOS Mu may be an effector enzyme for the dystrophin complex. H(+) + 2 L-arginine + 3 NADPH + 4 O2 = 4 H2O + 2 L-citrulline + 3 NADP(+) + 2 nitric oxide Binds 1 FAD. Binds 1 FMN. Tetrahydrobiopterin (BH4). May stabilize the dimeric form of the enzyme. Stimulated by calcium/calmodulin. Inhibited by n-Nos-inhibiting protein (PIN) which may prevent the dimerization of the protein. Inhibited by NOSIP (By similarity). Homodimer. Interacts with DLG4; the interaction possibly being prevented by the association between NOS1 and CAPON (By similarity). Forms a ternary complex with CAPON and RASD1 (PubMed:11086993). Forms a ternary complex with CAPON and SYN1 (By similarity). Interacts with ZDHHC23 (By similarity). Interacts with NOSIP; which may impair its synaptic location (By similarity). Interacts with HTR4 (PubMed:15466885). Interacts with VAC14 (By similarity). Interacts (via N-terminal domain) with DLG4 (via N-terminal tandem pair of PDZ domains) (PubMed:10623522). Interacts with SLC6A4 (PubMed:17452640). Forms a complex with ASL, ASS1 and SLC7A1; the complex regulates cell-autonomous L-arginine synthesis and citrulline recycling while channeling extracellular L-arginine to nitric oxide synthesis pathway (PubMed:22081021). In skeletal muscle, it is localized beneath the sarcolemma of fast-twitch muscle fiber by associating with the dystrophin glycoprotein complex. In neurons, enriched in dendritic spines (By similarity). Widely expressed in the nervous system: expressed in cerebrum, olfactory bulb, hippocampus, midbrain, cerebellum, pons, medulla oblongata, and spinal cord. Also found in skeletal muscle, where it is localized beneath the sarcolemma of fast twitch muscle fibers, and in spleen, heart, kidney, and liver. N-NOS-1 and N-NOS-2 are found in all parts of the nervous system. NNOS beta and gamma occur in a region-specific manner in the brain and NNOS beta expression is developmentally regulated. NNOS Mu is only found in mature skeletal and cardiac muscles. By cholinergic agonists acting at inositol phosphate-linked muscarinic receptors in cardiac myocytes. The PDZ domain in the N-terminal part of the neuronal isoform participates in protein-protein interaction, and is responsible for targeting nNos to synaptic membranes in muscles. Mediates interaction with VAC14 (By similarity). Ubiquitinated; mediated by STUB1/CHIP in the presence of Hsp70 and Hsp40 (in vitro). In MDX mice (mouse model of dystrophinopathy) the dystrophin complex is disrupted and nNOS is displaced from sarcolemma and accumulates in the cytosol. Belongs to the NOS family.