Z-Leu-Leu-Leu-vinyl sulfone

Inhibits the trypsin-like, chymotrypsin-like and caspase-like (PGPH) activity in isolated proteasomes and living cells by covalent modification of the amino-terminal threonine of the catalytically active β subunits. The vinyl sulfone acts as a Michael acceptor for soft nucleophiles such as thiols, leading to the formation of a covalent bond, while being resistant to attack by free thiols, which can cause inactivation of other classes of protease inhibitors.