Purification and Functional Analysis of Fungal Nitric Oxide Reductase Cytochrome P450nor

Cytochrome P450nor (P450nor) is a nitric oxide (NO) reductase involved in fungal denitrification. Denitrification is a biological process in which nitrate or nitrite is reduced to gaseous nitrogen, the reverse reaction of nitrogen fixation. It therefore plays an important role in maintaining global environmental homeostasis. The involvement of P450nor in fungal denitrification indicates that denitrification not only occurs in prokaryotic bacteria, but also in eukaryotic fungi. In addition, the reduction of NO to nitrous oxide catalyzed by P450nor has added new insight into the function of cytochrome P450s, which are usually monooxygenases. Currently, five isozymes of P450nor have been isolated from the subdivisions of eumycota, and studies on the function and structure of P450nor have provided important information for both molecular mechanisms of P450 reactions and wastewater treatment. This chapter describes the screening of NO reductase activities, cloning, purification, and functional analysis of P450nor.