Isolation and partial characterization of a hemolytic and toxic protein from the nematocyst venom of the Portuguese Man-of-War, Physalia physalis

Nematocysts isolated from the stinging tentacles of the Atlantic Portuguese Man-of-War (Physalia physalis) possess a potent venom composed of several proteins. A hemolytic protein lethal to mice has been isolated from this nematocyst venom. This protein, physalitoxin, appears to be responsible for both the venom's hemolytic and lethal activities. The hemolysin has a molecular weight of approx. 240 000, a sedimentation coefficient of 7.8 S, and is rod-like in shape with a calculated axial ratio of about 1 : 10. It appears to be composed of three subunits of unequal size, each of which is glycosylated. Two of these subunits seem to have pKi values near 8.2 and the third near 5.5. Physalitoxin comprises about 28% of the total nematocyst venom protein. It is 10.6% carbohydrate by weight and represents the major glycoprotein of the venom. Physalitoxin is inactivated by concanavalin A and this inactivation can be blocked with alpha-methyl-mannoside. The inactivation by concanavalin A is temperature-dependent about 12 degrees C and the hemolytic activity of untreated venom is temperature-dependent below 12 degrees C. Physalitoxin is the first hemolytic toxin from a cnidarian to be purified directly from isolated nematocysts.