Active Motif's Phenylmethylsulfonyl fluoride (PMSF) is a non-specific inhibitor of serine proteases and the cysteine protease papain (reversible by DTT treatment). PMSF does not inhibit metalloproteases, most cysteine proteases or aspartic proteases. PMSF is provided at a concentration of 100 mM in isopropanol. It is recommended to use a working concentration of 0.1 - 1 mM. Since protease levels may vary among cell and tissue types, it may be necessary to optimize the concentration of inhibitors to use.