Phosphorylation on amino acids, such as serine, threonine, and tyrosine results in the formation of a phosphoprotein, when the phosphate group of the phosphoprotein reacts with the -OH group of a Ser, Thr, or Tyr side chain in an esterification reaction.
Phosphorylation of tyrosine
Tyrosine phosphorylation requires the presence of protein tyrosine kinases (PTK) as well as protein tyrosine phosphatase (PTP) for activation. Tyrosine phosphorylation is fast to react and the reaction can be reversed. Being one of the major regulatory mechanisms in signal transduction - cell growth, differentiation, migration and metabolic homeostasis are cellular processes maintained by tyrosine phosphorylation. The function of protein tyrosine kinases and protein-tyrosine phosphatase counterbalances the level of phosphotyrosine on any protein. The malfunctioning of specific chains of protein tyrosine kinases and protein tyrosine phosphatase has been linked to multiple human diseases such as obesity, insulin resistance, and type 2 diabetes mellitus. Phosphorylation on tyrosine doesn't occur in just eukaryotes but has been discovered to occur in a selection of bacterial species and present among prokaryotes. Phosphorylation on tyrosine maintains the cellular regulation in bacteria similar to its function in eukaryotes.