Gamma-glutamyl cyclotransferase () (GGACT) is a ubiquitous enzyme found in bacteria, plants, and metazoans from Dictyostelium through to humans. It converts gamma-glutamylamines to free amines and 5-oxoproline [, , ]. It also degrades the cross-link between a lysine and a glutamic acid residue generated by transglutaminases. GGACT is structurally relatedto glutamylcyclotransferase (GGCT) [].