Seyfried NT, Xu P, Duong DM, Cheng D, Hanfelt J, Peng J. Systematic approach for validating the ubiquitinated proteome.
Anal Chem. 80(11):4161-9 (2008) 
Tagwerker C, Flick K, Cui M, Guerrero C, Dou Y, Auer B, Baldi P, Huang L, Kaiser P. A tandem affinity tag for two-step purification under fully denaturing conditions: application in ubiquitin profiling and protein complex identification combined with in vivocross-linking.
Mol Cell Proteomics. 5(4):737-48 (2006)