Purification, characterization, and biological activity of a substance P-related peptide from the gut of the Australian lungfish, Neoceratodus forsteri

Lu Liu*, J. Michael Conlon, Jean M P Joss, Elizabeth Burcher

*Corresponding author for this work

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

A peptide with mammalian substance P (SP)-like immunoreactivity was isolated from an extract of the spiral intestine of the Australian lungfish, Neoceratodus forsteri. The primary structure of this peptide was established as Lys-Pro-Arg-Pro-Asp-Glu-Phe-Tyr-Gly-Leu-Met · NH2, showing 64% identity with mammalian SP. In isolated preparations of lungfish foregut circular muscle, lungfish SP produced a slow, long-lasting tonic contraction, with a pD2 value of 8.19. Lungfish midgut circular muscle preparations responded to lungfish SP rapidly and in a more complex manner. There was an increase in the frequency of spontaneous activity (pD2 = 8.76), associated with diminished amplitude of the spontaneous contractions (pD2 = 9.24), also coupled in some preparations with a tonic contraction (pD2 = 8.43). The response patterns of foregut and midgut circular muscle to acetylcholine (ACh) were very similar to those seen to lungfish SP. Lungfish SP and ACh, however, had very weak effects on both foregut and midgut longitudinal muscle. These data demonstrate that lungfish SP may be a physiologically important regulator of gastrointestinal motility in Neoceratodus. This study further confirmed that the structures of SP-related peptides have been strongly conserved under the pressure of vertebrate evolution, particularly in preserving the functionally important sequence, Phe-Xaa-Gly-Leu-Met · amide, at the C-terminus. The sequence of lungfish SP is identical to that of bufokinin, a SP-related peptide previously isolated from the intestine of the cane toad, Bufo marinus, supporting the hypothesis that lungfishes and amphibians share a common ancestor.

Original languageEnglish
Pages (from-to)104-112
Number of pages9
JournalGeneral and Comparative Endocrinology
Volume125
Issue number1
DOIs
Publication statusPublished - 2002

Keywords

  • Circular muscle
  • Gastrointestinal activity
  • Gut
  • Lungfish
  • Substance P
  • Tachykinin

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