Historical perspectives on protein phosphorylation and a classification system for protein kinases

Abstract

Work on the phosphorylation of proteins as a dynamic process involved in the regulation of biological processes started in the 1950s with the finding that phosphorylaseaand phosphorylasebare phospho and dephospho forms of the same enzyme. The field expanded sharply in the late 1960s with the discovery of the cyclic-AMP-dependent protein kinase, and it is now clear that phosphorylation-dephosphorylation constitutes a major type of regulation almost as common as allosteric control. The protein kinases, which catalyse the phosphorylation step in various phosphorylationdephosphorylation systems, can be divided into two main classes, the serine-threonine protein kinases and the tyrosine protein kinases. Each class can be subdivided into groups or entities depending on the nature of the agent(s) that regulate activity.