A sulfated, myotropic neuropeptide termed leucosulfakinin (Glu-Gln-Phe-Glu-Asp-Tyr(SO3H)-Gly-His-Met-Arg-Phe-NH2) was isolated from head extracts of the cockroach Leucophaea maderae. The peptide exhibits sequence homology with the hormonally active portion of the vertebrate hormones human gastrin II and cholecystokinin, suggesting that these peptides are evolutionarily related. Six of the 11 amino acid residues (55 percent) are identical to those in gastrin II. In addition, the intestinal myotropic action of leucosulfakinin is analogous to that of gastrin.

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Two myotropic pcptidcs termed locustatachykinin I (Gly-Pro-or-Gly-Phe-Tyr-Gly-V~-~g-NH~) and locustatachykinin II (Ala-Pro-Leu-Ser-GlyPhe-Tyr-Gly-Val-Arg-NH,) were isolated from brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, Locusta migratoriu. Both peptides exhibit sequence. homologies with the vertebrate tachykinins. Sequence homology is greater with the 6sh and amphibian tachykinins (up to 45%) than with the mammalian tachykinins. In addition, the intestinal myotropic activity of the locustatachykinins is analogous to that of vertebrate tachykinins. The peptides discovered in this study may just be the first in a whole series of substances from arthropod species to be identified as tachykinin family peptides. Moreover, both chemical and biological similarities of vertebrate and insect tachykinins substantiate the evidence for a long evolutionary history of the ~chy~n peptide family.

Each residue of the insect kinin carboxy-terminal pentapeptide has a distinct role in conformational preference, specific receptor interactions or signal transduction. The beta-turn preference of residues Phe1-X2-X3-Trp4 implicates this as the bioactive conformation. The amidated carboxyl terminus, required for activity in many neuropeptide families, may be generally important for signal transduction and its inclusion may therefore be essential for agonist design.