Super‐Reduced Mechanism of Nitric Oxide Reduction in Flavo‐Diiron NO Reductases

Abstract

AbstractFlavo‐diiron nitric oxide reductases (FNORs) are non‐haem diiron proteins that protect anaerobic organisms against toxic nitric oxide by reducing it to nitrous oxide. The exact mechanism by which these enzymes operate is still unclear. Recent experimental evidence favors the diiron‐dinitrosyl mechanism involving [{FeNO}7]2 as a reactive intermediate in contrast to the previously suggested diiron‐mononitrosyl pathway. In this work a computational study of the diiron‐dinitrosyl, or the super‐reduced, mechanism has been undertaken and the key reactive intermediates have been identified. The two‐electron reduction of [{FeNO}7]2 to form [{FeNO}8]2 is confirmed as a key step for initiating the mechanism and leads to the instant formation of a hyponitrite adduct. The energy requirements for the formation of the intermediates competes well with the mono‐nitrosyl mechanism. This study provides an insight and a step forward towards gaining a better understanding of the mechanism of NO reduction by FNORs.