Fig. 4.

Forms I and II of rNosZ produced in E. coli. The observed difference in the spectroscopic signatures of individual preparations of rNosZ reflect in the composition of Cu_Z observed in the 3D structures. (A) Typically, isolated rNosZ contains a [4Cu:2S] center, in line with UV/vis properties of a form I enzyme (Fig. 3A). (B) In cases where spectroscopy indicated that the enzyme was obtained as form II (Fig. 2F), this was corroborated by the replacement of the bridging S_Z2 sulfide for a terminal H₂O molecule, leading to the [4Cu:S] center designated Cu^Z*.