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, E3 ligases or other proteins that contain ubiquitin-associated domains or ubiquitin-interacting motifs (UIMs). This product is formed with wild-type human recombinant ubiquitin and linkage-specific enzymes.