Fluor de Lys® Substrate is a highly sensitive and convenient alternative to radiolabeled, acetylated histones or peptide/HPLC methods for the assay of histone deacetylases. The Fluor de Lys® Substrate, which comprises an acetylated lysine side chain, is incubated with a sample containing HDAC activity (nuclear or cellular extract, purified enzyme, bead-bound immunocomplex, etc.). Deacetylation of the substrate sensitizes the substrate so that, in a second step, treatment with the Fluor de Lys® Developer produces a fluorophore. Histone deacetylases from all known classes have been successfully assayed with the Fluor de Lys® Substrate. These include human HDACs 1, 2, 3 and 8 (class I), human HDACs 4 and 9 (class II) and the sirtuins yeast Sir2, human SIRT1 and human SIRT2 (class III; reaction must include the sirtuin substrate NAD+). The substrate is cell-permeable and serves as the basis for the HDAC Cellular Activity Assay Kit (Prod. No. BML-AK503). NOTE: Must be used in conjunction with Fluor de Lys® Developer (Prod. No. BML-KI105). Sufficient for 100-1000 assays of HDACs or sirtuins (50 µl reaction volume, 50-500 µM (substrate).