THE CHARACTERISTICS OF THE EXOTOXIN Vm-Pm PRODUCED BY VIBRIO MIMICUS

Toxin Vm-Pm produced by Vibrio mimicus was purified in procedures as follows:salting out of ammonium sulfate,anion exchange chromatography on DEAE-cellulose and gel filtration chromatography of Sephadex G100.The purified toxin Vm-Pm gave a single band with a molecular weight of 30.456kD following SDS-PAGE with or without β-mercaptoethanol,indicating that the toxin Vm-Pm did not contain inter-chain disulphide bonds in its conformation and was a single-chain polypeptide.Amino acid composition analysis demonstrated that the toxin protein contained fifteen different kinds of amino acids and revealed a comparatively higher percentage of acidic amino acids(26.6%)than alkalic amino acids(14.4%).Hydrophobic amino acids corresponded to 33.4% of total amino acid residues.The optimal pH for the toxin was 6-8 and resistant to trypsase. Heat treatment at 56℃ and 100℃ abolished the hemolytic activity of the toxin.The toxin completely lost its activity when incubated at temperatures of 56℃ and 100℃ for 40min and 1min,respectively. The toxin showed unique characteristics as compared with other known bacterial toxins.