Isolation and characterisation of glutamate receptor antagonists from venoms of orb-web spiders.

Two distinct families of low-molecular-weight toxins (argiotoxins) have been isolated from the venom of the orb-web spider. Argiope trifasciata. The toxins have been purified to homogeneity and characterised by spectroscopic, mass spectrometric and microchemical analysis. The major biologically active member of the first family of toxins is 2,4-dihydroxyphenylacetyl-asparagine linked through a C11-tetra-amine to N-terminal arginine; other members of this family are methylene homologues. The second family of toxins possesses an indolic group in place of the 2,4-dihydroxyphenyl chromophore. The toxins act as non-competitive inhibitors at quisqualate-type glutamatergic receptors on a metathoracic retractor unguis nerve-muscle preparation of Schistocerca gregaria. The loss of the N-terminal arginine reduces biological activity of the first family of toxins, but not of the second. The nature of the polyamine appears to be less important, perhaps acting as a spacer between the cationic arginine and the more hydrophobic aromatic tail of the toxins.