A Fluor de Lys® fluorescent assay system. The HDAC6 Fluorescent Activity Assay/Drug Discovery Kit is a complete assay system designed to measure the lysyl deacetylase activity of the recombinant human HDAC6 included in the kit. The kit is ideal for chemical library screening for candidate inhibitors or activators or kinetic assay of the enzyme under varying conditions. The Fluor de Lys® HDAC6 assay is based on the Fluor de Lys® Substrate and Fluor de Lys® Developer combination. The assay procedure has two steps. First, the Fluor de Lys® Substrate, which comprises an acetylated lysine side chain, is incubated with HDAC6. Deacetylation of the substrate sensitizes the substrate so that, in the second step, treatment with the Fluor de Lys®Developer produces a fluorophore.