The FLUOR DE LYS-Green substrate offers a highly sensitive and convenient alternative to radiolabeled, acetylated histones or peptide/HPLC methods for the assay of histone deacetylases. The assay procedure has two steps. First, the FLUOR DE LYS-Green Substrate, which comprises an acetylated lysine side chain, is incubated with a sample containing HDAC activity (HeLa nuclear or other extract, purified enzyme, bead-bound immunocomplex, etc.). Deacetylation of the substrate sensitizes the substrate so that, in the second step, treatment with the FLUOR DE LYS Developer (BML-KI105) produces a fluorophore. The FLUOR DE LYS-Green substrate has a higher wavelength excitation and emission than the original FLUOR DE LYS substrate (BML-KI104). This avoids interference by quenching or fluorescence from compounds absorbing and/or emitting in the near UV and blue range. Formulation: 50mM solution in DMSO. Purity: ≥95% (HPLC). Long Term Storage: -80°C.