Array-based fluorescence assay for serine/threonine kinases using specific chemical reaction.

We report herein the development of an efficient fluorescence assay for serine/threonine kinases using a peptide array. Our approach is based on chemical reactions specific to phosphoserine and phosphothreonine residues, that is, base-mediated beta-elimination of the phosphate group and subsequent Michael addition of a thiol-containing fluorescent reagent. This procedure enables the covalent introduction of a fluorescent moiety into the phosphorylated peptide. Novel fluorescent reagents were designed for this purpose and synthesized. With these reagents, protein kinase A (PKA) and Akt-1 activities were readily detected. Our method can also be used to measure the activity of kinase inhibitors. This assay is expected to be widely applicable in kinase research.