Biological activities of prymnesin-2 isolated from a red tide alga Prymnesium parvum.

Previously we isolated prymnesin-1 (PRM1) and prymnesin-2 (PRM2) as the major hemolytic and ichthyotoxic agents in the red tide organism Prymnesium parvum and disclosed the structure of PRM2 as a novel glycoside with unusual multiple functionality. PRM2 caused 50% hemolysis of a 1% suspension of dog red blood cells at 0.5 nM. The potency exceeded that of plant saponin by 50000 times. The lethality of PRM2 on freshwater fish Tanichthys albonubes was comparable to that of brevetoxin and also the ichthyotoxicity was markedly enhanced by Ca2+ and by a slight elevation of pH: LC50 in a Ca2+ free medium (pH 7.0) was 300 nM and in the presence of 2 mM Ca2+ (pH 8.0) was 3 nM. The hemolytic activity of PRM2 was not affected by Ca2+ but was markedly affected by blood cell origin. Also, the observation of competitive inhibition by the PRM2 analogues allowed us to assume the presence of a specific binding site on the blood cell surface.