Selective destruction of skin permeability activity in cholera toxin: effect of acid on cholera enterotoxin

The effect of treatment of purified cholera enterotoxin with acid at pH 2.0 for 1 h followed by neutralization of the acid on the biological activity of the toxin was studied. It was found that the material loses 85 to 96% of its skin permeability activity and this loss is neither reversed nor increased after 28 days of storage at 5 to 10 C. Other biological properties such as diarrheagenic activity, lipolysis stimulating activity, and the lethal dose for mice remain unaffected by acid treatment. These observations indicate that the skin permeability activity is more sensitive to relatively minor changes in molecular structure than are the diarrheal, lipolytic, and mouse lethality activities.