NOS catalyzes the oxidization of L-arginine to produce L-citrulline and NO. Nitric oxide (NO) is an inorganic, gaseous free radical that carries a variety of messages between cells. Vasorelaxation, neurotransmission and cytotoxicity can all be enhanced throµgh cellular response to NO. NO production is mediated by members of the nitric oxide synthase (NOS) family. There are three types of NOS: two constitutive isoforms, brain or neuronal NOS (b or nNOS, type I) & endothelial cell NOS (eNOS, type III), and one inducible isoform (iNOS, type II). iNOS is found in a variety of cell types including macrophages, hepatocytes, synoviocytes, and smooth muscle cells. Cytokines such as interferon-gamma (IFN), tumor necrosis factor (TNF), interleukin-1 and -2, and lipopolysaccarides (LPS) cause an increase in iNOS mRNA, protein, and activity levels. The phosphorylation of eNOS by Protein kinase C was associated with an increase in NO production.