Conformational Changes of the Cholinergic Receptor Protein from Torpedo Marmorata as Revealed by Quinacrine Fluorescence
In chemical synapses the arriving pulse induces on the presynaptic side the release of a transmitter, which diffuses through the synaptic cleft and binds on the post-synaptic side to a receptor. Subsequent events involving an ionophore finally lead to the opening of ionic channels and a passive flow of ions results in a local discharge of the potential across the membrane (6). Electrophysiologica experiments have shown that the depolarizing effects of physiological transmitters can be mimicked by structurally related compounds (agonists), whereas a different class of compounds has the ability to inhibit reversibly the depolarizing action of agonists (antagonists). In recent years biochemical investigations have focussed on the acetylcholine receptor for which nicotine is an agonist and d-tubocurarine is an antagonist (3, 11). This receptor is found, for example, in the neuromuscular junction and in large quantities in the electric organ of some fish species. It has been found that snake a-toxins, which block in vivo the function of the postsynaptic membrane, bind with high affinity and specificity to biochemical preparations of the receptor (2). The use of these toxins has made possible considerable progress in the field of preparation of the receptor, and one can now study the interesting questions concerning the functional events in the receptor system.
KeywordsLocal Anesthetic Conformation Change Equilibration Process Membrane Fragment Fluorescence Increase
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