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

Nitrous oxide (N 2 O) is a potent greenhouse gas that accumulates in the atmosphere due to anthropogenic N 2 O emissions, disrupting the nitrogen balance. N 2 O reductase (N 2 OR) in denitrifying bacteria contributes to the nitrogen cycle by converting N 2 O to molecular nitrogen as a last step. For the reduction of N 2 O during denitrification, electron donors must supply two electrons. This review discusses the in vivo physiological electron donors involved in the reduction reaction of N 2 OR: cytochrome c 55X and pseudoazurin, as well as the non-physiological electron donors commonly used in N 2 OR studies: reduced MV/BV, dithionite, and ascorbate. The kinetic parameters of the connection between N 2 OR and the electron donors are also included. This aim of this review to gain further insight into the reduction mechanism of N 2 OR, presenting the electron transfer center, Cu A , and the catalytic center, Cu Z , of N 2 OR. The state changes of Cu site have a significant impact on electron transfer and N 2 O 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 N 2 OR. Modulating the electron transfer pathways of N 2 OR holds promise as an approach to decreasing N 2 O emissions. Graphical abstract