2.7. 20S Proteasome Activity Assay

The 20S proteasome, the catalytic core of the 26S proteasome complex, is responsible for the degradation of short-lived regulatory proteins, including Nrf2 and IκB [7, 11, 12]. Since MG132 mainly inhibits proteasome chymotrypsin (ChT)-like activity [13], we detected 20S proteasome activity by quantifying the hydrolysis of SLLVY-AMC, a fluorogenic substrate for the ChT-like activity, according to the manufacturers' procedures of the 20S proteasome activity assay kit (Millipore). Detailed operation procedures have been described in our early studies [6].