Purification and Characterization of Substance P-related Peptide from the Body of the African Lungfish,Protopterus dolloi

摘要

The peptide with structural similarity to mammalian substance P(M-SP)has been isolated from extract of the body of the African lungfish,Protopterus dolloi,using the rectum of the newt as the bioassay system.The primary structure of the SP-related peptide was identified as Lys-Pro-Arg-Pro-Asp-Gln-Phe-Tyr-Gly-Leu-Met-NH_2(L-SP)and contained four substitutions(Lys~1 -> Arg,Arg~3 -> Lys,Asp5 -> Gln,and Tyr~8 -> Phe)compared with M-SP;this structure is identical to that of the peptide isolated from the gut of the Australian lungfish.Circular dichroism spectra showed that L-SP had an unordered structure in the buffer solution and phospholipid bilayers.This peptide was found to have an excitatory effect on rectal muscle tissues of newt,quail,and fish.L-SP also had a more potent vasodilatory effect on the guinea-pig aorta than that of M-SP.The identification of the peptide provides evidence that SP family,hitherto confined to mammals,have a widespread occurrence in lungfish.