Catalyzes the conversion of L-arginine to L-citrulline producing nitric oxide (NO) which is a messenger molecule with diverse functions throughout the body (PubMed:7568075, PubMed:12804606). Truncated isoforms (isoform 3-isoform 6) are able to form intracellular complexes with the full-length protein and serve as dominant negative inhibitors of the enzyme activity. H(+) + 2 L-arginine + 3 NADPH + 4 O2 = 4 H2O + 2 L-citrulline + 3 NADP(+) + 2 nitric oxide Binds 1 FAD. Binds 1 FMN. Stimulated by calcium/calmodulin. Isoform 3 is expressed in larvae only. Isoform 4, isoform 5, isoform 6 and isoform 10 are expressed throughout development from embryos to adults. Belongs to the NOS family.