To obtain the Cu-metalloproteins, one equivalent of Cu(NO3)2 was added directly to the Bpycontaining SCP proteins. Copper binding was confirmed by UV-Vis spectroscopy which clearly showed a red shift in the π-π* transition of the Bpy ligand in the presence of Cu(II), consistent with previous reports on copper binding to Bpy-containing proteins . Titration experiments confirmed that, at the concentrations of interest (20-100 µM), Cu(II) bound to the Bpycontaining SCP proteins with ~1:1 stoichiometry (see ESIa, Figures and). Copper binding was also confirmed by ICP-MS analysis (see ESIa).