Patent ID: 8518660

Claim:
A diubiquitin for measuring the isopeptidase activity of a deubiquitinase comprising: A) a first ubiquitin molecule operably linked to at least one first energy transfer pair member; and B) a second ubiquitin molecule operably linked to at least one second energy transfer pair member; wherein said first ubiquitin molecule is operably linked to said second ubiquitin molecule by an isopeptide bond from the C-terminus of said first ubiquitin molecule to the side chain of a lysine residue of said second ubiquitin molecule, wherein said first and second energy transfer pair members are individually either a fluorescent group or a quenching group, wherein said first and second ubiquitin molecules comprise a cysteine residue at any position between residues 8 and 70, and wherein said first and second energy transfer pair members are attached to said first and second ubiquitin molecules at said cysteine residues.