Bio-scale Engine: Reaction Mechanism of Nitric Oxide Reductase Cytochrome P450nor from Fusarium oxysporum

A unique enzyme mechanism named a bio-scale engine was proposed for a nitric oxide reductase, cytochrome P450nor (P450nor). P450nor has some structural similarities with a combustion engine: the heme pocket, the heme and NADH correspond to a combustion chamber, a piston head, and a spark plug, respectively. Each putative step of this reaction occurred in the heme pocket was characterized using HartreeFock calculations. The MO analysis revealed that the NO ligand dissociates from the heme immediately after one-electron reduction by NADH. Analysis of the MO energy revealed that NADH acts as a one-electron reducer, not as a two-electron reducer. Our results divulged that all reaction steps are too fast to become ratelimiting. Therefore, the rate-limiting steps are the process of inhaling NO and NADH into the heme pocket and the process of exhaust a reaction product. Kinetics of these processes was discussed based on a large-amplitude vibration, which helps inhaling and exhaust processes in a heme pocket. The reaction mechanism proposed can explain the published experimental data consistently. Key-Words: Cytochrome P450nor, Nitric oxide reductase, Quantum chemical calculation, Reaction mechanism, Electron transfer