 The proteasome is a protein complex responsible for the bulk of proteolysis in the cell, as well as proteolytic activation of certain protein substrates.It was the first non-peptidic proteasome inhibitor discovered and is widely used as a research tool in biochemistry and cell biology.It covalently modifies the amino-terminal threonine of specific catalytic subunits of the proteasome, a discovery helped to establish the proteasome as a mechanistically novel class of protease