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

The effect of loss of the 34-kDa periplasmic NosX protein on the properties of N2O reductase was investigated with an N2O-respiration negative, double mutant of the paralogous genes nosX and nirX of Paracoccus denitrificans. In spite of absence of whole-cell N2O-reducing activity, the purified reductase was catalytically active, which attributes NosX a physiological role in sustaining the reaction cycle. N2O reductase exhibited the spectroscopic features of CuA and the redox-inert, paramagnetic state, CuZ∗, of the catalytic center. CuZ∗, hitherto considered the result of spontaneous reaction of the reductase with dioxygen, attains cellular significance.