Purification of and kinetic studies on a narrow specificity synaptosomal membrane pyroglutamate aminopeptidase from guinea‐pig brain

Abstract

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 μM 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 μM. Copyright © 1985, Wiley Blackwell. All rights reserved