The isolation of endogenous modulators of the affinity of acetylcholinesterase to cholinergic ligands.

By help of a batchwise affinity chromatography procedure the binding of cholinergic ligands to AChE obtained from caudate nucleus from calf brain was studied. The affinity of edrophonium to a crude as compared to a pure enzyme was about 50 times higher. After addition of material isolated from the crude preparation the enzyme was changed to the high affine form. The dissociation constant of the crude enzyme-edrophonium complex determined in the affinity chromatographic experiments was 1.5 X 10(-5) M and in enzymatic experiments 1.8 X 10(-7) M. It is proposed that there is present in mammalian neuronal tissue a factor that increases the affinity of certain cholinergic ligands to a site other than the catalytic site on AChE.