Phenylmethanesulfonylfluoride (PMSF)

PMSF is a serine protease inhibitor commonly used in the preparation of cell lysates. PMSF does not inhibit all serine proteases[citation needed]. It is rapidly degraded in water and stock solutions are usually made up in anhydrous ethanol, isopropanol, corn oil, or DMSO.PMSF binds specifically to the active site serine residue in a serine protease. It does not bind to any other serine residues in the protein. This is a result of the hyperactivity of that serine residue caused by the specific environmental conditions in the enzyme's active site. Because PMSF binds covalently to the enzyme, the complex can be viewed by X-ray crystallography; it can therefore be used as a chemical label to identify an essential active site SER in an enzyme. PMSF is commonly used in protein solublization in order to deactivate proteases from digesting proteins of interest after cell lysis.