Toxic, antimicrobial and hemagglutinating activities of the purple fluid of the sea hare aplysia dactylomela rang, 1828

Brazilian Journal of Medical and Biological Research (1998) 31: 785-791 Biological activity of the purple fluid of the sea hare ISSN 0100-879X

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Toxic, antimicrobial and hemagglutinating activities of the purple fluid of the sea hare Aplysia dactylomela Rang, 1828
V.M.M. Melo1, A.M. Fonseca1, I.M. Vasconcelos2 and A.F.F.U. Carvalho1 Departamentos de 1Biologia and 2Bioquímica e Biologia Molecular, Universidade Federal do Ceará, Fortaleza, CE, Brasil

Abstract
Correspondence
V.M.M. Melo Departamento de Biologia Universidade Federal do Ceará 60455-760 Fortaleza, CE Brasil Fax: [phone]

Received July 11, 1997 Accepted March 26, 1998

The antimicrobial, hemagglutinating and toxic activities of the purple fluid of the sea hare Aplysia dactylomela are described. Intact or dialyzed purple fluid inhibited the growth of species of Gram-positive and Gram-negative bacteria and the action was not bactericidal but bacteriostatic. The active factor or factors were heat labile and sensitive to extreme pH values. The fluid preferentially agglutinated rabbit erythrocytes and, to a lesser extent, human blood cells, and this activity was inhibited by the glycoprotein fetuin, a fact suggesting the presence of a lectin. The fluid was also toxic to brine shrimp nauplii (LD50 141.25 µg protein/ml) and to mice injected intraperitoneally (LD50 201.8 ± 8.6 mg protein/kg), in a dose-dependent fashion. These toxic activities were abolished when the fluid was heated. Taken together, the data suggest that the activities of the purple fluid are due primarily to substance(s) of a protein nature which may be involved in the chemical defense mechanism of this sea hare.

Key words
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Aplysia Antimicrobial Purple fluid Toxicity Hemagglutinating activity

Introduction
Many sea hares, which are opistobranch molluscs, discharge a fluid from the purple gland when disturbed. This reaction suggests that this fluid contains bioactive factors which may act against