Protease inhibitor cocktails (similar to Sigma P8849) are commonly used in protein extraction to prevent protein breakdown by natural cellular proteases. These enzymes (including cysteine, serine, acid proteases, and aminopeptidases) are activated when cells or tissues are disrupted and can damage target proteins. This ready-to-use 100X DMSO solution uses a mix of inhibitors (AEBSF, Bestatin, E-64, Leupeptin, Pepstatin A) to block such proteases, preserving proteins’ natural structure and properties. Being EDTA-free, it works well for downstream steps sensitive to divalent cations, like phosphorylation analysis or enzyme assays.