Ac-Arg-Gly-Lys(Ac)-AMC is a fluorogenic peptide substrate primarily used in coupled enzyme assays for detecting histone deacetylase (HDAC) activity. In these assays, HDACs remove the acetyl group from the lysine residue, enabling subsequent cleavage by trypsin-like proteases at the lysine-AMC bond, which releases the fluorescent reporter 7-amino-4-methylcoumarin (AMC). The fluorescence can be quantitatively measured using spectroscopy (excitation ~370 nm, emission ~440 nm). This substrate is also suitable for direct assays of certain trypsin-like protease activities. Its design enhances selectivity for acetyl-modifying enzymes, making it invaluable in epigenetic research, HDAC inhibitor screening, studies of enzyme kinetics, and analysis of deacetylation in cell lysates or purified preparations.