Isolation and sequence of canine xenopsin and an extended fragment from its precursor.

Canine xenopsin and a 27 residue segment of its precursor immediately surrounding the xenopsin moiety were isolated from acidic extracts of stomach. The six C-terminal residues of canine xenopsin, H-Phe-His-Pro-Lys-Arg-Pro-Trp-Ile-Leu-OH, were identical to those in Xenopus xenopsin less than Glu-Gly-Lys-Arg-Pro-Trp-Ile-Leu-OH. The amino acid sequence determined for the segment of the precursor was similar to the corresponding region of Xenopus pro-xenopsin (approximately 33% homology) and to the related Xenopus precursors, pro-levitide, pro-PGLa, pro-magainin and pro-caerulein. These results, indicating evolutionary conservation of xenopsin and a portion of its precursor, suggest that this peptide has important biologic function(s).