Isolation and chemical characterization of a novel insulin‐related neuropeptide from the freshwater snail, Lymnaea stagnalis

Abstract

A novel molluscan insulin‐related peptide (MIP) III, has been isolated from alcohol extracts of the neurohaemal area of the cerebral neuroendocrine light‐green neurones of Lymnaea stagnalis. MIP III was purified by sequential high‐performance gel‐permeation chromatography followed by reverse‐phase HPLC. MIP III is a heterodimer connected by disulphide bonds. Edman degradation analysis and subsequent alignment with the A and B chains of the previously identified MIP I and II showed that the 24‐amino‐acid peptide with the sequence pQSRPSIVC(E)CCFNQCTVQ(E)LLAYC represents the MIP III A chain, and the 37‐amino‐acid peptide sequence TTQHTCSILSRPHPRGLCGSTLANMVQWLCSTYTTSS the B chain. The overall amino acid sequence of MIP III shows about 50% similarity with those of MIP I and II, and only 20–40% similarity with other peptides of the insulin superfamily. Important structural features, e.g. disulphide bridges and the hydrophobic core, are conserved in MIP III. Copyright © 1992, Wiley Blackwell. All rights reserved