This family of enzymes EC:2.3.2.5 catalyse the cyclization of free L-glutamine and N-terminal glutaminyl residues in proteins to pyroglutamate (5-oxoproline) and pyroglutamyl residues respectively [1]. This family includes plant and bacterial enzymes and seems unrelated to the mammalian enzymes.

1: Carica papaya glutamine cyclotransferase belongs to a novel plant enzyme subfamily: cloning and characterization of the recombinant enzyme. Dahl SW, Slaughter C, Lauritzen C, Bateman RC Jr, Connerton I, Pedersen J; Protein Expr Purif 2000;20:27-36. PMID:11035947