Elucidating electron transfer pathways in N2OR catalysis for mitigation of N2O emissions: a comprehensive review

Nitrous oxide (N₂O) is a potent greenhouse gas that accumulates in the atmosphere due to anthropogenic N₂O emissions, disrupting the nitrogen balance. N₂O reductase (N₂OR) in denitrifying bacteria contributes to the nitrogen cycle by converting N₂O to molecular nitrogen as a last step. For the reduction of N₂O during denitrification, electron donors must supply two electrons. This review discusses the in vivo physiological electron donors involved in the reduction reaction of N₂OR: cytochrome c_55X and pseudoazurin, as well as the non-physiological electron donors commonly used in N₂OR studies: reduced MV/BV, dithionite, and ascorbate. The kinetic parameters of the connection between N₂OR and the electron donors are also included. This aim of this review to gain further insight into the reduction mechanism of N₂OR, presenting the electron transfer center, Cu_A, and the catalytic center, Cu_Z, of N₂OR. The state changes of Cu site have a significant impact on electron transfer and N₂O binding. Moreover, the review focuses on potential electron transfer pathways and binding sites in the electron donor → Cu_A → Cu_Z process, along with the steady-state turnover in the Cu_Z site. Additionally, the review explains the commonly used methods in mechanistic studies of N₂OR. Modulating the electron transfer pathways of N₂OR holds promise as an approach to decreasing N₂O emissions.

Graphical abstract