STRUCTURAL CHARACTERIZATION OF A DIURETIC PEPTIDE FROM THE CENTRAL-NERVOUS-SYSTEM OF THE LEECH ERPOBDELLA-OCTOCULATA - ANGIOTENSIN-II AMIDE

Purification of a material immunoreactive to an antiserum against angi otensin II and present in the central nervous system of the pharyngobd ellid leech Erpobdella octoculata was performed by reversed-phase high pressure liquid chromatography combined with both enzyme-linked immun osorbent assay and dot immunobinding assays for angiotensin II. Establ ishment of the amino acid sequence by Edman degradation, electrospray, and fast atom bombardement mass spectrometry measurements and enzymat ic treatment by carboxypeptidase A indicated that this ''central'' ang iotensin II-like material, the first one fully characterized in the an imal kingdom, is an angiotensin II amide. This finding constitutes als o the first biochemical characterization of a peptide of the angiotens in family in an invertebrate. Synthetic angiotensin II amide exerts, w hen injected in leeches, a diuretic effect and is, 1 and 2 h postinjec tion, 100-fold more potent than vertebrate angiotensin II. An identifi cation of the proteins immunoreactive to an antiserum against angioten sin II performed at the level of both central nervous system extracts and in vitro central nervous system-translated RNA products indicated that in the two cases, two proteins were detected. Their molecular mas ses, which were, respectively, similar to 14 and similar to 18 kDa for the central nervous system extracts and similar to 15 and similar to 19 kDa for in vitro central nervous system-translated RNA products, di ffer from that of angiotensinogen (similar to 60 kDa), the precursor o f vertebrate angiotensin II.