Alpha-bungarotoxin binding in the central nervous system of Limulus polyphemus

The binding of 125I-labelled alpha-bungarotoxin in the central nervous system of the horseshoe crab, Limulus polyphemus, was investigated. Comparative binding studies in various tissues of L. polyphemus demonstrated a selective association of the toxin with nervous tissues. The greatest enrichment of toxin binding in subcellular fractions of brain tissue was observed in a fraction enriched in mitochondria and acetylcholinesterase-containing membranes. Autoradiographic studies revealed the localization of alpha-bungarotoxin binding to the longitudinal connectives and neuropile regions of the abdominal ganglia. Three toxin binding components with approximate sedimentation coefficients of 9 S, 15.4 S and 17.4 S were present in solubilized extracts of brain tissue. 125I-labeled alpha-bungarotoxin binding to these components was inhibited 72%, 47%, 9% and 0% by 10 microM concentrations of (+)-tubocurarine, nicotine, scopolamine and pilocarpine, respectively. The apparent formation of the 15.4 S and 17.4 S proteins from the 9 S protein was obtained. The 15.4 S and 17.4 S components are suggested as aggregates of the 9 S protein. This 9 S protein is proposed as an acetylcholine receptor from the central nervous system of L. polyphemus.