L-proline, by itself or in animal tissue extracts, inhibits the response of the sea anemone Anthopleura elegantissima to the alarm phermone, anthopeurine. 2. The effect of proline is mediated by a receptor that is specific for the structure and configuration of the part of the L-proline molecule containing the carboxyl and imino groups. 3. Proline inhibition is competitive, in the sense that the effects of a given proline concentration can be overridden by an increase in anthopeurine concentration. 4. The magnitude of proline inhibition increases with proline concentration and decreases as the duration of exposure to proline increases. 5. Neither the final conducting system mediating the alarm response nor the responding muscles are inhbited by proline. Inhibition presumably occurs at or soon after the level of anthopleurine receptors. 6. Proline inhibition may resolve the potential conflict between Anthopleura's mutually exclusive feeding and alarm pheromone responses.
