Histone acetylases (HAT’s) and Histone deacetylases (HDAC’s) are associated with regulation of gene expression. In general, increased levels of histone acetylation are associated with increased transcriptional activity, whereas decreased levels of acetylation are associated with repression of gene expression. HDAC’s are localized in both the cytosol and nucleus and some shuttle between the nucleus and cytosol. Increased HDAC expression has been observed in various cancers.The PromoKine HDAC Activity Assay Kit provides a direct, fast, fluorescence-based method to measure the in situ HDAC activity. The procedure requires two easy steps, all performed in the same cell culture plate. First, the cell permeable HDAC Substrate, which comprises an acetylated lysine side chain, is incubated with cells grown in a 96-well plate. Inside the cells, HDAC deacetylates the substrate. The second step involves lysing the cells and treating with the Developer that produces a fluorophore from the Deacetylated HDAC Substrate. The generated fluorescence can be quantified at Ex/Em = 368/442 nm. The assay is well suited for high throughput screening applications.