BGSN3 is a good substrate for the SNAP- tag ? and H 5 enzymes . The activities of SNAP- tag ? and H 5 enzymes on BGSN3 are reasonable (IC 50 =17.8 and 10 μM, respectively). BGSN3 is a click chemistry reagent, it contains an Azide group and can undergo copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing Alkyne groups. It can also undergo strain-promoted alkyne-azide cycloaddition (SPAAC) reactions with molecules containing DBCO or BCN groups.