FIGURE 7.

PcuC binds one Cu(I) ion via His⁷⁹, Met⁹⁰, His¹¹³, and Met¹¹⁵. A, UV-visible spectra of incremental addition of apo-PcuC (wild type) to a 7.5 μm Cu(BCS)₂³⁻ solution. Spectra were taken when 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.6, and 2.0 protein equivalents/copper atom were added. The arrows indicate the direction of the absorption change after the protein addition. B, incremental addition of apo-PcuC(M90A) to a 7.5 μm Cu(BCS)₂³⁻ solution is shown as an example. An analogous behavior was observed for the other substituted versions of PcuC (data not shown). C, plot of A₄₈₃ against the ratio of PcuC wild type (closed circles), PcuC(H79A) (open circles), PcuC(M90A) (squares), PcuC(H113A) (triangles), PcuC(M115A) (diamonds), and PcuC(H113A/M115A) (crosses) to total Cu(I). Saturation is observed only when PcuC (wild type) was used in the experiment.