The 20S proteasome is the proteolytic core of a large protein degradation complex, the 26S proteasome. Proteasome inhibitors exhibit anti-inflammatory and antiproliferative effects, evidence that the proteasome may be an important drug target for the treatment for cancer and inflammatory diseases. Cayman’s 20S Proteasome Assay employs a specific 20S substrate, SUC-LLVY-AMC which, upon cleavage by the active enzyme, generates a highly fluorescent product with an emission wavelength at 480 nm.