Purification of and kinetic studies on a narrow specificity synaptosomal membrane pyroglutamate aminopeptidase from guinea-pig brain.
A pyroglutamate aminopeptidase activity, distinct from that of cytoplasm, was released from a synaptosomal membrane preparation of guinea-pig brain by papain treatment. This activity was further purified 3560-fold relative to the homogenate with a yield of 17% by a procedure involving gel filtration chromatography, calcium phosphate cellulose chromatography and hydrophobic interaction chromatography on phenyl-Sepharose CL-4B. The purified synaptosomal pyroglutamate aminopeptidase hydrolysed only thyroliberin, acid-thyroliberin, the luliberin N-terminal tripeptide (Glp-His-Trp) and, only slightly, Glp-His-Gly. No hydrolysis was observed with dipeptides containing N-terminal pyroglutamic acid (Glp) or with pyroglutamyl peptides containing more than three amino acids. A Km value of 40 microM was recorded when thyroliberin was used as substrate; however, luliberin was found to inhibit the hydrolysis of thyroliberin competitively with a Ki value of 20 microM.
O'Connor
B
B
O'Cuinn
G
G
D000626:Aminopeptidases / Q000302:isolation & purification*; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000201:enzymology*; D002845:Chromatography / Q000379:methods; D004586:Electrophoresis / Q000379:methods; D005615:Freezing; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology; D011751:Pyroglutamyl-Peptidase I / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D013379:Substrate Specificity; D013574:Synaptosomes / Q000201:enzymology*; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism
D010455:Peptides; D013973:Thyrotropin-Releasing Hormone; D000626:Aminopeptidases; D011751:Pyroglutamyl-Peptidase I