Purification and Characterization of [Ala2]-Neuromedin N from the Visceral Tissue of the African Lungfish, Protopterus dolloi

摘要

A new biologically active peptide with structural similarity to neuromedin N (NMN) has been isolated from extracts of visceral tissue of the African lungfish, Protopterus dolloi, using the rectum of the quail as the bioassay system. The primary structure of NMN-related peptide was established as Lys-Ala-Pro-Tyr-Ile-Leu-OH ([Ala2]-NMN) and contained one substitution (Ala2 ℃ Ile) compared with the porcine NMN. [Ala2]-NMN was found to have an excitatory effect on rectal muscle tissues of quail (Coturnix japonica), newt (Cynops pyrrhogaster) and black bass (Micropterus sulmoides). The threshold concentration of [Ala2]-NMN for contraction of C. japonica muscle was found to be approximately 10-11 M. [Ala2]-NMN showed contractile activities in the following order: C. japonica > C. pyrrhogaster > M. sulmoides. The identification of [Ala2]-NMN provides evidence that NMN family, hitherto confined to mammals, has a widespread occurrence in lungfish.