Phenylmethanesulfonyl Fluoride (PMSF) is a serine protease inhibitor commonly used in protein purification and biochemical studies to prevent protein degradation. By inhibiting serine proteases, PMSF preserves protein integrity during cell lysis, extraction, and other procedures where proteases could otherwise degrade proteins of interest. PMSF is a potent, irreversible inhibitor of serine proteases, such as trypsin, chymotrypsin, and thrombin. Due to its rapid inactivation in aqueous solutions, PMSF is typically prepared fresh and added to lysis buffers and other protein solutions just before use. PMSF is soluble in organic solvents such as ethanol, isopropanol, and DMSO but has limited water solubility.