Allosteric effects of phenyltrimethylammonium and propidium on acetylcholinesterase active site.

Different spin labelled fluorophosphates and fluorophosphonates with different chain length were investigated with respect to their sensitivity to the allosteric changes of acetylcholinesterase active site produced by phenyltrimethylammonium (Pta) or d-tubocurarine (TC); only fluorophosphates were found to be sensitive to these changes. Therefore fluorophosphates were chosen also for the study of allosteric effects of propidium. The addition of Pta and propidium to spin labelled membrane acetylcholinesterase of the Torpedo marmorata electric organ decreased maximal hyperfine splitting of the EPR spectrum, indicating that the microgeography of the acetylcholinesterase active site is usually changed in a way which increases the freedom of motion of the spin label's piperidine ring. TC alone did not change the EPR spectrum, but it prevented the influence of Pta and not that of propidium.