PATCH labeling in the BSA through red light

For the liquid chromatography-mass spectrometry (LC-MS) analysis, the 500 μM AP was used to label BSA in the reaction, followed by clicking chemical conjugation with 0.1 mM azide-PEG3-biotin under 0.5 mM CuCl(2), 2 Mm Tris (3-hydroxypropyltriazolylmethyl) amine (THPTA, Sigma-Aldrich) and 5 mM ascorbic acid. Then, the identification of the labeled site was analyzed by a HF-X mass spectrometer (ThermoFisher) that was coupled to a nano Elute liquid chromatography system (Bruker Daltonics). MS data were processed by the Byonic software 4.0.12 version (Protein Metrics INC.) for both de novo sequencing and database search. The peptides with scores higher than 200 were retained for analysis.