IA-alkyne (2.5-10 μM; 1 hour) can react with cysteines. Soluble fractions of HeLa cell lysates (2.0 mg/ml) are treated with IA-alkyne. Labeled proteome samples are conjugated with a fluorescent rhodamine-azide tag through CuAAC, and analyzed by SDS-PAGE. In-gel fluorescence imaging reveals that IA-alkyne has a strong fluorescent intensity.