Abstract
Abstract A novel bioactive peptide was isolated from the brain of the Japanese crucian carp, Carassius auratus langsdorfii, by using the intestine of the fish as the bioassay system. The primary structure of the peptide was determined to be KPRPHQFIGLMamide. The sequence was found to be highly homologous to the fish substance P-related peptides isolated from Atlantic cod and rainbow trout. We designated the peptide Carassius Substance P (Caa-SP). Caa-SP was identical with the peptide whose presence was inferred from a cDNA analysis by other investigators. Caa-SP exerted an excitatory effect on visceral muscle tissues of fish with the threshold at about 3 × 10−9 M. The peptide enhanced the ERG b-wave, depolarized the dark membrane potential and slightly decreased the amplitude of S-potentials of the L-type horizontal cells in the carp retina.
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