Purification and characterization of Contractin A from the pedicellarial venom of sea urchin, Toxopneustes pileolus

A component that causes contraction of the isolated guinea pig tracheal smooth muscle was isolated in homogeneous form from the venom of the pedicellaria of the sea urchin, Toxopneustes pileolus. It is named Contractin A. Contractin A has 18,000 Da with a total residue of 138 amino acids. The molecular weight is about 17,700. The N-terminal amino acid is serine. The partial amino acid sequence was determined up to 37 residues. Direct comparison of sea urchin Contractin A does not show any similarity in amino acid sequence to toxins isolated from other marine toxin producers such as sea snakes, sea anemones, or marine worms. Contractin A caused contraction of the tracheal smooth muscle in a dose-dependent manner. Furthermore, Contractin A relaxed the contraction induced by histamine. The contraction and relaxation activity of Contractin A on the tracheal smooth muscle is reduced by a cyclooxygenase inhibitor such as indomethacin. The contraction induced by Contractin A is also inhibited by a phospholipase C inhibitor but not by a phospholipase A2 inhibitor. These results suggest that in the isolated guinea pig tracheal smooth muscle, the response to Contractin A may be effected through activated phospholipase C.