Tissue transglutaminase，a 78-kDa calcium dependent enzyme (EC 2.3.2.13)，is found both in the intracellular and the extracellular spaces of various types of tissues. TG2 crosslinks proteins between the ε-amino group of a lysine residue and the γ-carboxamide group of glutamine residue，creating an inter- or intramolecular bond that is highly resistant to proteolysis (protein degradation). TG2 also possesses deamidation，GTP-binding/hydrolyzing，and isopeptidase activities. Intracellular TG2 is thought to play an important role in apoptosis，while extracellular TG2 has been linked to cell adhesion，ECM stabilization，wound healing，receptor signaling，cellular proliferation，and cellular motility.
