Antipain

Antipain is an oligopeptide isolated from actinomycetes and used in biochemical research as a protease inhibitor, reported in 1972 as the first natural peptide containing a ureylene group. Specifically, it is an inhibitor of trypsin and papain.

It has been crystallised in complex with carboxypeptidase from wheat and Leishmania major oligopeptidase B. In both cases the backbone carbonyl of the terminal arginine of antipain forms a covalent bond to the active site serine in the protease.