Protein phosphorylation causes the addition of a phosphate group onto serine, threonine or tyrosine amino-acid residues of proteins. Phosphorylations are precise reversible changes that are used to regulate intracellular events such as protein complex formation, cell signaling, cytoskeleton remodeling and cell cycle control. Consequently, protein kinases, which are responsible for the phosphorylations, play an important role in controlling protein function, cellular machine regulation and information transfer through cell signaling pathways. Kinase activities therefore have definitive regulatory effects on a broad variety of biological processes, in which activated kinases typically target a large number of different substrate proteins. There are over 500 protein kinases encoded in the human genome, and it is approximated that 40% of all proteins are phosphorylated at some stage in different cell types and at different cell states (Manning et al., 2002). Furthermore, kinases regulate each other through phosphorylation, resulting in a complex web of regulatory relations (Ma'ayan et al., 2005).