Oligomeric and polymeric protein associations often involve purely secondary chemical forces that is, hydrogen bonds, ionic bonds and van der Waals forces. Protein assembly and disassembly can also be regulated by post-translational modifications, such as phosphorylation or dephosphorylation, even in these cases the subunits are not linked covalently. The first transglutaminase enzyme (TGase, EC 2.3.2.13) was recognised on the basis of its ability to catalyse the covalent incorporation of amine into proteins.