NosX function connects to nitrous oxide (N₂O) reduction by affecting the Cu_Z center of NosZ and its activity in vivo

The effect of loss of the 34‐kDa periplasmic NosX protein on the properties of N 2 O reductase was investigated with an N 2 O‐respiration negative, double mutant of the paralogous genes nosX and nirX of Paracoccus denitrificans . In spite of absence of whole‐cell N 2 O‐reducing activity, the purified reductase was catalytically active, which attributes NosX a physiological role in sustaining the reaction cycle. N 2 O reductase exhibited the spectroscopic features of Cu A and the redox‐inert, paramagnetic state, , of the catalytic center. , hitherto considered the result of spontaneous reaction of the reductase with dioxygen, attains cellular significance.