Endosulfine, endogenous ligand for the sulphonylurea receptor: Isolation from porcine brain and partial structural determination of the α form

Abstract

Anti-diabetic sulphonylureas act via high affinity binding sites coupled to K-ATP channels. Endosulfine, an endogenous ligand for these binding sites, was shown to exist in two molecular forms, α and β, in both the pancreas and the central nervous system. We describe here the isolation, and partial structural characterization of α endosulfine derived from porcine brains by means of a series of chromatography runs and gel electrophoresis. Porcine α endosulfine is a protein with a molecular mass of 13,196 daltons as determined by mass spectrometry and which is N-terminally blocked. Tryptic digestion followed by separation of the fragments by HPLC and automated Edman degradation yielded a total of 72 amino acids in four partial sequences. Comparison of these sequences with that present in the National Biomedical Research Foundation protein data bank indicated a 82% identity with a 112-amino acid protein with a molecular mass of 12,353 daltons called 'cyclic AMP-regulated phosphoprotein-19', isolated from the bovine brain as a substrate for protein kinase A.