Nitric oxide (NO) is a product of nitric oxide synthase (NOS). NOS catalyzes the oxidation of L-arginine to form NO. NO plays important roles in the cardiovascular, nervous and immune systems. To form NO, there must be an electron transfer between the oxygenase and reductase domains. The electron flows from NADPH to FAD, FMN and the oxygenase domain heme during catalysis. The NO that is released can be further oxidized to form nitrite, while heme-NO complex can also be converted to nitrate. 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 isoforms. Experiments using NO donor (NOC-12) are still undergoing.