Reversible post-translational modification of amino acids or proteins is a common phenomenon in biological systems. For instance, () can be phosphorylated by a (). Also, phosphorylated this amino acid can be dephosphorylated by a ().
OC, methytransferase, kinase
OS, kinase, phosphatase
OY, phosphatase, kinase
OP, phosphate transferase, dephosphatase