What is PMSF?

PMSF (phenylmethanesulfonylfluoride or phenylmethylsulfonyl fluoride) is a serine protease inhibitor commonly used to prepare cell lysates. PMSF is specific in its binding to the active serine residue site in a serine protease, but not other serine residues in the protein. Since PMSF binds covalently to the enzyme at the active serine residue, the complex can be visualized by X-ray crystallography. Therefore PSMF can be used as a chemical label for identification of essential active SER site in an enzyme.