Covalent modification is the alteration of a synthesized protein facilitated by a catalyst. The structure and function of the protein is modified, changing its role in cellular regulation.
Covalent modifications involve the addition or removal of chemical groups on a protein and may involve a single or multiple amino acids. Modifications can be reversible and irreversible. Irreversible modifications are more energy-intense as they require the synthesis of a new protein. Irreversible modifications are associated with physiological cascade processes. Reversible reactions are seen in metabolic processes and signaling regulation. Reversible reactions often require different enzymes to complete the reaction in the forward and reverse direction.