Characterization of the Ptychodiscus brevis Polyether Neurotoxin Binding Component in Excitable Membranes.
Annual rept. 1 Jun 86-31 May 87,
MIAMI UNIV CORAL GABLES FLA
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The polyether lipid-soluble toxins isolated from the marine dinoflagellate Ptychodiscus brevis formerly Gymnodinium breve bind to a unique site, Site V, associated with voltage-dependent sodium channels in rat brain synaptosomes. Using tritiated PbTx-3 as a specific probe for binding at Site V, a Kd of 2.9 nM and a Bmax of 6.8 pmolesmg synaptosomal protein has been determined. Binding equilibria and displacement by unlabeled PbTx-3 occur in a comparable concentration range to that of saxitoxin site I. Labeled toxin can be displaced in a competitive manner by any of the other 5 naturally-occuring toxins the quantitative displacement ability of each appears to reflect individual potency in fish bioassay. Preliminary Ki calculations have been made for four of the toxins. Two separate photoaffinity probes have been synthesized and have been synthesized and have been covalently-linked to PbTx-3. Each complete photoaffinity-toxin conjugate competitively displaces tritiated PbTx-3 from its specific binding site, with approximate ED50s in the 20-50 nM concentration ranges.