Nitric oxide (NO) is a product of nitric oxide synthase (NOS). NOS catalyzes the oxidation of L-arginine, which then forms L-citrulline and NO in cells. NO is important as it plays a role in many systems in the body such as the cardiovascular, nervous, and immune systems. The domain structure of NOSs includes the oxygenase and the reductase domains. To form NO, there must be an electron transfer between these two domains. Starting in the reductase domain, the electron begins at NADPH, then flows to FAD, FMN, and transfers to the oxygenase domain heme during catalysis. A dimer must be formed for the electron transfer to the heme. The heme then binds to O2,which starts the reactions of the NO synthesis. The NO that is released can be further oxidized to form nitrite (productive cycle), while heme-NO complex can also be converted to nitrate (futile cycle). Three different NOS isoforms (endothelial NOS (eNOS), cytokine-inducible NOS (iNOS), and neuronal NOS (nNOS)) have been identified and characterized. Interestingly, they exhibit different catalytic profiles. Through our research, we will focus on the percentage of nitrite and nitrate productions that occur in the three NOS isoforms. Our preliminary data indicated that more nitrate than nitrite was produced in both iNOS and nNOS. Experiments using NO donor (NOC-12) are still undergoing.