Biotin-Ahx-Ub-PA (UbiQ-076) is an activity-based probe for deubiquitinating enzymes (DUBs) and contains propargyl amide (PA) as an electrophile. UbiQ-076 is labeled on the N-terminus with biotin. An aminohexanoic acid linker is used to create extra space between the biotin and Ub protein for efficient access of biotin binding entities. UbiQ-078 can be used for activity profiling experiments and determining DUB inhibitor specificity. The C-terminal PA electrophile has two characteristics: 1) It forms a covalent linkage with (the active site Cys residue of) a DUB that can be cleaved by acid treatment (5% aq. TFA), allowing for proteomic analyses. 2) It targets all three major DUB families: UCH, USP and OTU.