The PARP1 Colorimetric Activity Assay Kit is designed to measure PARP1 activity for screening and profiling applications. PARP1 is known to catalyze the NAD-dependent addition of poly(ADP-ribose) to histones. The key to the PARP1 Colorimetric Activity Assay is the biotinylated substrate. With this kit, only three simple steps are required for PARP1 reactions. First, histone proteins are coated on a 96-well plate. Next, the PARP1 biotinylated substrate is incubated with an assay buffer that contains the PARP1 enzyme. Finally, the plate is treated with streptavidin-HRP followed by addition of the colorimetric HRP substrate to produce color that can then be measured using a UV/Vis spectrophotometer microplate reader.