Produces nitric oxide (NO) which is a messenger molecule with diverse functions throughout the body (PubMed: 7531687, PubMed: 7544004). In macrophages, NO mediates tumoricidal and bactericidal actions. Also has nitrosylase activity and mediates cysteine S-nitrosylation of cytoplasmic target proteins such PTGS2/COX2 (By similarity). As component of the iNOS-S100A8/9 transnitrosylase complex involved in the selective inflammatory stimulus-dependent S-nitrosylation of GAPDH on 'Cys-247' implicated in regulation of the GAIT complex activity and probably multiple targets including ANXA5, EZR, MSN and VIM (PubMed: 25417112). Involved in inflammation, enhances the synthesis of proinflammatory mediators such as IL6 and IL8 (PubMed: 19688109).