ANANTIN - A PEPTIDE ANTAGONIST OF THE ATRIAL-NATRIURETIC-FACTOR (ANF) .2. DETERMINATION OF THE PRIMARY SEQUENCE BY NMR ON THE BASIS OF PROTON ASSIGNMENTS

Anantin, a naturally occurring peptide from Streptomyces coerulescens, binds competitively to the receptor of atrial natriuretic factor (ANF) from bovine adrenal cortex (K(d) = 0.6-mu-M) and acts as ANF antagonist. Protein chemical data and FAB-MS have identified anantin to be a cyclic polypeptide consisting of 17 common L-amino acids. The molecule is highly stable and precludes the application of standard sequencing methods. The primary sequence of anantin was determined by 2D H-1 NMR spectroscopy and the application of advanced protein chemical methods to be Gly1-Phe2-Ile3-Gly4-Trp5-Gly6-Asn7-Asp8-Ile9-Phe10-Gly11-His12-Tyr13-Ser14-Gly15-Asp16-Phe17. The molecule is cyclized between the beta-carboxyl group of Asp8 and the amino group of Gly1.