Mg 132 z lll cho

Peptide FRET substrates with ten glutamine residues were procured from GenScript (Piscataway, NJ, USA); the substrate with five glutamine residues was purchased from Peptide Protein Research Ltd. (Fareham, UK). The standard fluorescent substrates for proteasome assays (N-succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin, Suc-LLVY-AMC) and HIV protease substrate 1 (Arg-Glu(EDANS)-Ser-Gln-Asn-Tyr-Pro-Ile-Val-Gln-Lys(Dabcyl)-Arg) were from Sigma-Aldrich (St. Louis, MO, USA) and Invitrogen (Carlsbad, CA, USA), respectively. Ac-RLR-AMC and Z-LLE-AMC were from UBPBio (Dallas, TX, USA). Bortezomib was from LC Laboratories (Woburn, MA, USA), MG-132 (Z-LLL-CHO), leupeptin (as hemisulfate salt), and marizomib was from Sigma-Aldrich, and Z-P-nLeu-D-CHO was from Enzo Life Science (Farmingdale, NY, USA). All other reagents were of the highest quality available or for molecular biology grades and were used without additional purification.