Peptide analogs of the mud crab pumping pheromone: structure–function studies

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Abstract
In the mud crab, Rhithropanopeus harrisii (Gould), larval release is highly synchronous and is controlled by peptide pheromones released from the hatching eggs. The pheromones and synthetic peptide analogs, containing neutral amino acids at the arnino-terminus and a basic amino acid at the carboxy-terminus, evoke larval release or pumping behavior in the female. Here we describe structure–function relationships between behavioral responses and peptide analogs of the pumping pheromone. Compounds tested included 11 peptides containing 1–7 neutral amino acid residues and a carboxy-terminal arginine residue, and modified arginine compounds. Complex feeding-stimulant mixtures and groups of peptides were tested to provide information about the number of different types of receptors. Pumping behavior was described in terms of response threshold, maximum percentage response and effective concentration range. All carboxy-terminal arginine peptides tested evoked pumping responses. Response thresholds ranged from 10-15 M for the most potent peptide Ile-Gly-Arg to 10-8 M for the least potent Tyr-Arg. Effective concentration ranges for the peptides varied from one to four orders of magnitude and the responses normally declined with further increase in concentration. Maximum percentage response was largely independent of response threshold and ranged from 30–60%, comparable to assay responses of larval hatch water. Responses within size groups of peptides were more similar than between groups. Studies with modified arginines showed that hydrophobic structures similar in size and shape to small peptides evoked responses. Sterically hindered hydrophobic moieties were ineffective. Tests with mixtures of active compounds support the hypothesis that there is one type of pumping peptide receptor.