The phosphorylation and dephosphorylation of proteins is a vital means of regulation. Protein kinases attach phosphoryl groups, whereas phosphatases remove the phosphoryl group from the target protein. What is the energy cost of this kind of covalent regulation?
Phosphorylation and dephosphorylation are the most common means of covalent modification.
It is important to note that phosphorylation and dephosphorylation are not the reverse of one another; each is essentially irreversible under physiological conditions.