Proteasome Activity Assay Kit (ab107921) takes advantage of the chymotrypsin-like activity, using an AMC-tagged peptide substrate (Proteasome Substrate (Succ-LLVY-AMC in DMSO), which releases free, highly fluorescent AMC (Ex/Em 350/440 nm) in the presence of proteolytic activity. Proteasome Activity Assay ... (2 g of protein for chymotrypsin-like activity and 7 g for caspase- and trypsin-like activities) was subjected to a

The kit provides purified 20S proteasome and is designed to test for Chymotrypsin-like activity (Suc-LLVY-AMC), Caspase-like activity of the proteasome subunits ß1/PSMB6 (LLE-AMC), and Chymotrypsin-like activity of ß5/PSMB5 (WLA-AMC). Results: Treatment of MM cells with MLN2238 predominantly inhibits chymotrypsin-like activity of the proteasome and induces accumulation of ubiquitinated proteins. MLN2238 inhibits growth and induces apoptosis in MM cells resistant to conventional and bortezomib therapies without affecting the viability of normal cells. The caspase-like (β1), trypsin-like (β2) and chymotrypsin-like (β5) activities of the 20S proteasome were determined using the fluorogenic substrates (Z)-LLE-AMC, Bz-VGR-AMC and Suc-Leu-Leu-Val-Tyr-AMC, respectively. The effect of celastrol on 20S proteasome activity was assayed following the protocol provided by the manufacturer.