Protein phosphorylation is a reversible posttranslational modification catalyzed by protein kinases and reversely by protein phosphatases. There are about 500 protein kinases and 25-30 phosphatases in human genome. Each kinase and phosphatase targets multiple substrates. Thus, protein phosphorylation is a most versatile signaling regulatory mechanism and constitutes a most complicated signaling network in living organisms. In fact, protein phosphorylation governs all aspects of physiological and pathological processes in human health
