Phenylmethyl sulphonyl fluoride ≥98 %, for biochemistry General, irreversible inhibitor of serin proteases (chymotrypsin, trypsin and thrombin) and for the dystin-protease papain. Inhibiton by sulphonation of the serine localised in the enzymatic active site. Reversible inhibitor of cysteine-proteases. K i = 0.91 ±0.01 mM Directions for use Working concentration: 17-174 µg/ml (0,1-1 mM). Dissolves easily in isopropanol, ethanol and methanol. Not stable in aqueous solutions (half-life value of 1 h at pH 7.5/RT). For stock solutions of 200-250 mM heat shortly (approx. 30 mins) to 30 °C. Stock solutions should be stored at -20 °C. Short term storage of few weeks may be done at +4 °C in the dark. PMSF reacts with thiols. DTT and β-mercaptoethanol reduce the inhibitory effect. At every stage of isolating or purifying the proteins, PMSF should be added fresh from the stock solution. PMSF is often not sufficient as the only protease inhibitor in the preparation to protect against decomposition processes, as for example high salt concentration (3.0 M) impairs the inhibitory effect of PMSF.