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 pK_i 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 α-methyl-mannoside. The inactivation by concanavalin A is temperature-dependent above 12°C and the hemolytic activity of untreated venom is temperature-dependent below 12°C. Physalitoxin is the first hemolytic toxin from a cnidarian to be purified directly from isolated nematocysts.