A synthetic peptide that irreversibly inhibits activity of caspase-3 and related caspases and blocks apoptosis. The inhibitor is designed as a methyl ester to enhance cell permeability. The conjugation with biotin allows detection of activated caspases in conjunction with avidin-tags. (CAUTION: If the intended use is on purified or recombinant enzymes, esterase should be added to generate free carboxyl groups).