Linkage specific di-Ub is a substrate for enzymes that cleave the isopeptide linkage between two ubiquitin molecules. It can also be used to investigate mechanism of binding and recognition by E1 or E2 enzymes, deubiquitinating enzymes (DUBs), E3 ligases or other proteins that contain ubiquitin-associated domains (UBAs) or ubiquitin-interacting motifs (UIMs). This product is formed with wild-type human recombinant ubiquitin and linkage-specific enzymes. Whereas K48-linked Ub chains mediate proteasomal degradation, and K63-linked Ub chains act in non-proteolytic events, the roles of unconventional poly-ubiquitin chains (linked through K6, K11, K27, K29, or K33) are not yet well understood. These non-canonical linkages are abundant in vivo and they may also target proteins for degradation. Ubiquitination through K11 is also important for endoplasmic reticulum-associated degradation (ERAD) and there undoubtedly exist DUBs that may have specificity for K11 linkages. This product is synthesized with wild-type ubiquitin.