We have developed a new molecular probe called CuR. This probe is selectively activated by labile Cu(I), hence enabling labeling of the proteins in Cu(I)-rich cellular environments. We applied CuR to ATP7A-WT and ATP7A-KO cells that were pretreated with or without Cu(gtsm). Next, we enriched the labeled proteins by immunoprecipitation, digested them with trypsin, and analyzed them using liquid chromatography-tandem mass spectrometry. We used label-free quantification in the mass spectrometry analysis to detect changes in labeled proteins caused by exogenous copper compared to the non-copper-treated condition.