title: An enzyme(s) that converts glutaminyl-peptides into pyroglutamyl-peptides. Presence in pituitary, brain, adrenal medulla, and lymphocytes.
abstract: The mechanism for the post-translational conversion of glutamine to pyroglutamic acid on the N terminus of newly synthesized peptides and proteins is unknown. An assay is reported that permits measurement of the rate of conversion of Gln-His-Pro-NH2 to pyroGlu-His-Pro-NH2 (TRH). Using this assay, we demonstrate that the spontaneous cyclization of the N-terminal glutamine of this peptide occurs only slowly under physiological conditions. Furthermore, we describe the presence in rat brain, porcine pituitary, and human B lymphocytes of an enzyme(s) which converts Gln-His-Pro-NH2 into pyroGlu-His-Pro-NH2. The enzyme(s) appears to be a glycoprotein, is maximally active at neutral pH, has a Mr of 55,000, and contains catalytically significant sulfhydryl groups. The product of the enzymatic reaction was confirmed by high resolution fast atom bombardment-mass spectrometry. In preliminary studies, we find that over 90% of the enzyme in bovine adrenal medulla is contained in the soluble chromaffin vesicle fraction. These findings indicate that in vivo the post-translational conversion of a glutaminyl-peptide into a pyroglutamyl-peptide is neither spontaneous nor abiotic as has been previously proposed.
mesh_terms: D000217:Acyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D000313:Adrenal Medulla / Q000201:enzymology*; D019881:Aminoacyltransferases; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002846:Chromatography, Affinity / Q000379:methods; D002848:Chromatography, DEAE-Cellulose / Q000379:methods; D007700:Kinetics; D008214:Lymphocytes / Q000201:enzymology*; D013058:Mass Spectrometry; D010902:Pituitary Gland / Q000201:enzymology*; D013552:Swine
chemical_list: D000217:Acyltransferases; D019881:Aminoacyltransferases; C059280:glutaminyl-peptide cyclotransferase