| Abstract: | The neurotoxic complex (Cb) from the venom of Pseudocerastes fieldi consists of an acidic non-toxic subunit (CbI) and a basic toxic one (CbII). The complex is only partially dissociated by salt-gradient chromatography; the two components are completely separable in the presence of urea. Chromatofocusing of CbI resulted in two protein peaks, both of which potentiated toxicity of CbII. CbI inhibits hemolysis induced by CbII, but not the phospholipase A2 activity of CbII. CbI reveals phospholipase A activity with non-micellar dithiolecithin, however, it shows no activity with micellar lecithin. The amino acid composition of CbI and its enzymatic activity, as well as the structural homology with A2 phospholipases of nontoxic subunits from other presynaptic neurotoxins may suggest that, a catalytic activity of the non-toxic subunits plays a role at the target site. |
