Ubiquitin is a highly conserved protein that plays a major role in the ubiquitination pathway, which is conserved from yeast to mammals. Ubiquitination, the conjugation of ubiquitin to other proteins through a covalent bond between its C-terminal glycine and the ε-amino group of lysine residues or the α-amino group of an N- terminal methionine onto proteins is essential for many cellular processes primarily linked to protein degradation. This process involves three steps with specific groups of enzymes in an ATP depended manner, which are activation with ubiquitin-activating enzymes (E1s), conjugation with ubiquitin-conjugating enzymes (E2s) and ligation with ubiquitin ligases (E3s). This Europium Cryptate Ubiquitin is ideal for measuring Ub chain conjugation or deconjugation using TR-FRET measurement. Its TR-FRET pair is Cy5-Ubiquitin.