Protein–Surfactant interactions in the defensive skin secretion of the Red Sea trunkfish Ostracion cubicus

With the aid of column chromatography, solvent fractionation and toxicity assays we made the following observations. (1) The defensive skin secretion of the Red Sea trunkfish Ostracion cubicus consists, on a dry weight basis, of about 15% proteins, of 5 to 70 kDa molecular weight. (2) The proteins serve as an integral part of the chemical defense mechanism and fulfill two essential roles: (a) as ichthyotoxins which affect fish through external application into the surrounding water; and (b) as modifiers/regulators of the action of the well-known active ingredient of trunkfish secretion, the cationic, quaternary-ammonium, surfactant pahutoxin (PHN). The latter, when isolated from other components, plays only a limited role in ichthyotoxicity. (3) The regulatory role is performed by nontoxic, and as yet unidentified, proteins which potentiate PHN ichthyotoxicity. Potentiation is presumably preceded and mediated by the protein–PHN association, suggesting a guiding “pharmacokinetic” role of the regulatory proteins. (4) Finally, it may be concluded that the entire secretion process functions with unique pharmacological complexity due to the multiplicity of active substances and their interdependency. Received: 7 May 1998 / Accepted: 7 June 1999