The Catalytic Center in Nitrous Oxide Reductase, CuZ, Is a Copper−Sulfide Cluster

Abstract
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 CuZ. This comprises a cluster of four copper ions bound by seven histidines and three other ligands modeled in the X-ray structure as OH- or H2O. However, elemental analyses and resonance Raman spectroscopy of isotopically labeled enzyme conclusively demonstrate that CuZ has one acid-labile sulfur ligand. Thus, nitrous oxide reductase contains the first reported biological copper−sulfide cluster.