CHEMBL5733425

Apoptosis Signal-Regulating Kinase Assay: The assay measures the phosphorylation level of a biotinylated peptide substrate by the ASK1 kinase using HTRF detection. This is a competitive, time-resolved fluorescence resonance energy transfer (TR-FRET) immunoassay, based on HTRF® KinEASE™-STK manual from Cisbio. Test compound, 1 μM STK3 peptide substrate, 4 nM of ASK1 kinase were incubated with 10 mM MOP buffer, pH. 7.0 containing 10 mM Mg-acetate, 0.025% NP-40, 1 mM DTT, 0.05% BSA and 1.5% glycerol for 30 minutes then 100 μM ATP was added to start the kinase reaction and incubated for 3 hr. Peptide antibody labeled with 1× Eu3+ Cryptate buffer containing 10 mM EDTA and 125 nM Streptavidin XL665 were added to stop the reaction and phosphorylated peptide substrate was detected using Envision 2103 Multilabeled reader from PerkinElmer. The fluorescence was measured at 615 nm (Cryptate) and 665 nm (XL665) and a ratio of 665 nm/615 nm was calculated for each well. The resulting TR-FRET level (a ratio of 665 nm/615 nm) was proportional to the phosphorylation level. Under these assay conditions, the degree of phosphorylation of peptide substrate was linear with time and concentration for the enzyme.