SUPERPOTENT SYNTHETIC TRIPEPTIDE MIMICS OF THE MUD-CRAB PUMPING PHEROMONE

Soluble pheromones released by the mud crab, Rhithropanopeus harrisii (Gould) during egg hatching cause the female crab to contract her abdo men rapidly (the pumping response). This stereotypical behavior can be induced in the laboratory by exposing egg-bearing females to solution s containing certain amino acids or peptides. Twelve amino acids exhib ited response thresholds of 10(-3)-10(-10) M, the most potent (norleuc ine, methionine and tryptophan) having a hydrophobic sidechain. Four s ynthetic tripeptides of the form Gly-X-Arg, where the hydrophobic resi due X was isoleucine, norleucine, methionine or phenylalanine, were su perpotent agonists over a limited concentration range. Gly-Ile-Arg was a significant agonist at 10(-17) and 10(-16) M, both Gly-Nle-Arg and Gly-Met-Arg at 10(-20) and 10(-19) M, and Gly-Phe-Arg at 10(-21), 10(- 20) and 10(-19) M. At the subattomolar concentration of 10(-20) M the superpotent pheromone mimics Gly-Met-Arg and Gly-Phe-Arg produced not only a statistically significant increase in the relative number of pu mping mud crabs but also a substantial increase in the pumping rate ra tio. In contrast, at 10(-13) m the tripeptide Gly-Met(O)-Arg with an i nternal residue of methionine sulfoxide blocked the abdominal pumping response of egg-bearing mud crabs. (C) Munksgaard 1993.