Alpha endosulfine is a novel molecule, structurally related to a family of phosphoproteins.

We have observed that alpha endosulfine, the 13KDa form of the endogenous ligand for sulfonylurea receptor recently isolated from porcine brain, displays strong similarities with a phosphoprotein of similar size previously isolated from bovine brain and called ARPP-19. To determine whether the two proteins are different entities, we developed an RT-PCR strategy for analyzing the main portion of bovine alpha endosulfine. We show that alpha endosulfine and ARPP-19 are different entities from the same family of proteins, coded by distinct genes.

Endosulfine, endogenous ligand for the sulphonylurea receptor: isolation from porcine brain and partial structural determination of the alpha form.

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, alpha and beta, in both the pancreas and the central nervous system. We describe here the isolation, and partial structural characterization of alpha endosulfine derived from porcine brains by means of a series of chromatography runs and gel electrophoresis. Porcine alpha 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.

Endosulfine, an endogenous peptidic ligand for the sulfonylurea receptor: purification and partial characterization from ovine brain.

Antidiabetic sulfonylureas act through receptors coupled to ATP-dependent potassium channels. Using the binding of [3H]glibenclamide, a highly potent sulfonylurea, to rat brain membranes to follow the purification procedure, we extracted from ovine brain, purified, and partially characterized two peptides that are endogenous ligands for the central nervous system sulfonylurea receptors. These peptides, referred to as alpha and beta endosulfine, differ by their isoelectric points, the beta form being more basic. Each form of endosulfine is recognized equally by the sulfonylurea receptors from the central nervous system and from insulin-secreting beta cells. In the same concentration range that is active on the receptors, beta endosulfine releases insulin from a beta-cell line. Endosulfine is a good candidate for being implicated in the physiology of beta cells and their disorders (e.g., type II diabetes) and in certain pathologies related to modifications of ion fluxes.

An endogenous ligand for the central sulfonylurea receptor.

An endogenous ligand for the rat central sulfonylurea receptor has been evidenced in the rat central nervous system. The characteristics of this ligand (extractibility, non-dialysability, chromatographic behaviour on different media, sensitivity to proteases) indicate that it is a neutral to slightly basic peptide.