Periplasmic nitrate reductase (Nap) is one of the most important bacterial nitrate reductases and are found in all phyla of bacteria. This family of enzymes contains the molybdenum cofactor in the active site, and in Nap, catalyzes the reaction of nitrate to nitrite. We believe that in pathogenic organisms they play an important role in nitrogen metabolism, and can use nitrate as an electron acceptor. Our research is focused on understanding the structure-function roles of Nap from pathogenic organisms such as Campylobacter jejuni and E. coli. To this end, we have cloned and overexpressed the catalytic subunit NapA, and working to express its paired electron donating heme, NapB. We investigate the properties of NapA and its Moco active site using a wide variety of techniques such as steady state kinetics and HPLC.