The catalytic center in nitrous oxide reductase, Cu-z, is a copper-sulfidecluster

The crystal structure of nitrous oxide reductase, the enzyme catalyzing the final step of bacterial denitrification in which nitrous oxide is reduced to dinitrogen, exhibits a novel catalytic site, called Cu-z. This comprises a cluster of four copper ions bound by seven histidines and three other li gands modeled in the X-ray structure as OH- or H2O. However, elemental anal yses and resonance Raman spectroscopy of isotopically labeled enzyme conclu sively demonstrate that Cu-z has one acid-labile sulfur ligand. Thus, nitro us oxide reductase contains the first reported biological copper-sulfide cl uster.