Part A. Protein Kinase-Mediated Phosphorylation Events Protein kinases (ATP:protein phosphotransferases) regulate a wide range of cellular events, including the transduction of signals leading to cell growth. Although the protein kinase superfamily encompasses a large and structurally diverse group of enzymes, protein and DNA sequencing data indicate that they share a common evolutionary origin with a particularly highly conserved catalytic core structure and function. At present, the well characterized protein kinases (PK) can be divided into four main subclasses
