Protein kinases transfer phosphate groups from ATP to serine, threonine, or tyrosine residues on protein peptide substrates, directly affecting the activity and function of the target. Radiolabel studies suggest that approximately 30% of proteins in eukaryotic cells are subject to phosphorylation. Kinase activity, a crucial post-translational modification, regulates a broad range of cellular activities including the cell cycle, differentiation, metabolism, and neuronal communication. In addition, abnormal activity of Akt, ERK, JNK, PKC, PKA, p38, and other MAPK are implicated in many disease states. R&D Systems offers a range of quality products for the detection of protein phosphorylation, which include kinase activity assays, phospho-specific antibodies, ELISA, and more.