Properties of radiolabeled alpha-bungarotoxin derivatives and their interaction with nicotinic acetylcholine receptors.
Column-purified monoiodinated, diiodinated, and tritiated derivatives of alpha-bungarotoxin (alpha-Bgt) are distinguished on the basis of their ultraviolet absorption and circular dichroism (CD) spectra. The pattern of changes in CD spectra on incorporation of iodine into a single tyrosine residue of alpha-Bgt and the widespread wavelength distribution of these effects are interpreted as reflecting primary chemical modification of the tyrosine chromophore as well as vicinal and global secondary structural changes. Native and tritiated alpha-Bgt are shown to be more effective than iodinated alpha-Bgt derivatives in competing for specific toxin binding sites on putative nicotinic acetylcholine receptors (nAChR) derived from rat brain reflecting functional perturbation of the modified toxin. In contrast, both membrane-bound and solubilized nAChR from Torpedo californica electroplax display little or no specific binding preference for native toxin, nor are there significant differences in lethal potency of alpha-Bgt derivatives toward mice. These results suggest that peripheral and putative central nAChR may differ in their alpha-Bgt binding properties and suggest the usefulness of modified toxin in detecting those subtle differences.
D000818:Animals; D001921:Brain / Q000378:metabolism; D002038:Bungarotoxins / Q000378:metabolism* / Q000633:toxicity; D002942:Circular Dichroism; D007457:Iodine Radioisotopes; D008297:Male; D051379:Mice; D008968:Molecular Conformation; D051381:Rats; D011950:Receptors, Cholinergic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D014316:Tritium
D002038:Bungarotoxins; D007457:Iodine Radioisotopes; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic; D014316:Tritium