FIGURE 3.

CueO is readily activated by externally added copper. A, exemplary spectroscopic assay of DMP-oxidase activity with apo-CueO from cytoplasm. Note that the enzyme was inactive until CuSO₄ was added (indicated by an arrow), which activates the enzyme without requirement of additional factors (solid line). In the negative control, CuSO₄ was added to an assay lacking enzyme (dotted line). Assay specifications: CueO, 0.6 μm; CuSO₄, 250 μm; DMP, 1 mm; activity, 1.5 units/mg. B, CueO DMP oxidase activity depends on external copper concentrations. The diagram shows the specific activity of DMP oxidation at a range of copper concentrations. All data points are corrected for non-enzymatic copper effects and reflect the result of five replicates. The standard deviation is indicated.