Bacteriostatic and cytolytic activity of purple fluid from the sea hare

A bacteriostatic factor, aplysianin P, was purified from the purple fluid of a sea hare, Aplysia kurodai, as a glycoprotein of 60 K daltons. A cytolytic glycoprotein purified from the purple fluid of Dolabella auricularia did not show antibacterial activity. Aplysianin P was half-maximally active for gram-positive and -negative bacteria at 0.2-5.8 micrograms/mL and its action was not bactericidal but bacteriostatic. Aplysianin P completely inhibited the syntheses of DNA and RNA by E. coli, but it did not induce the release of ATP from bacteria. These results suggest that aplysianin P, found in an invertebrate, the sea hare, is a new bacteriostatic protein and that it exerts its action by inhibiting nucleic acid syntheses, as a DNA-inhibiting, chemotherapeutic drug does.