Radiolabeled alpha-bungarotoxin derivatives: kinetic interaction with nicotinic acetylcholine receptors.
The binding interactions of purified tritiated [3H]-alpha-Bgt and monoiodinated and diiodinated derivatives of alpha-bungarotoxin with membrane-bound nicotinic acetylcholine receptors (nAChR) from Torpedo californica electroplax and rat brain have been characterized by several kinetic and equilibrium techniques. By all criteria, [3H]-alpha-Bgt and 125I-labeled monoiodinated alpha-Bgt ([125I]-alpha-Bgt) exhibited comparable specificities and affinities for nAChR. In contrast, affinity of nAChR for 125I-labeled diiodinated alpha- Bgt ([125I2]-alpha-Bgt) was reduced, and [125I2]-alpha-Bgt-nAChR complexes showed anomalous biphasic dissociation kinetics. [125I]-alpha-Bgt and [125I2]-alpha-Bgt binding was inhibited most potently by native alpha-Bgt as opposed to iodinated toxins. [3H]- alpha-Bgt was the radiotoxin most resistant to inhibitory influences. The use of well-characterized, chemically modified alpha -Bgt derivatives may identify ligand binding microheterogeneities and tissue-specific receptor subclasses.
D000818:Animals; D001921:Brain / Q000378:metabolism; D002038:Bungarotoxins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004557:Electric Organ / Q000378:metabolism; D007553:Isotope Labeling; D007700:Kinetics; D051381:Rats; D011950:Receptors, Cholinergic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014101:Torpedo
D002038:Bungarotoxins; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic