Purity >98%. The calpains are a family of calcium-dependent cysteine proteases, with calpain I (μ-calpain) requiring micromolar calcium and calpain II (m-calpain) requiring millimolar calcium. Ac-calpastatin (184-210) is an acetylated synthetic peptide from human calpastatin that strongly inhibits both calpains I and II but not papain (a cysteine protease) or trypsin (a serine protease). This 27 amino acid peptide is encoded by exon 1B of Ac-calpastatin (184-210) and corresponds to a portion of inhibitory domain 1.