Abstract— By incubating the particulate fraction of caudate nucleus from calf brain in ion‐free media, about 90 per cent of the AChE activity was brought into solution. The effects of different salts, EDTA and tetracaine on the release were studied. The mol. wt. of the enzyme was determined by gel filtration. About 90 per cent of the activity in a fresh preparation appeared in a form with mol. wt. 80,000. During storage this form was gradually transformed into forms with higher mol. wts. The effects of changes in the ionic environment on the aggregation were investigated. Purification attempts always resulted in the transformation of the enzyme into high mol. wt. forms. If the release was performed in the presence of DEAE‐Sephadex‐A25, the enzyme no longer aggregated. The cytosol fraction always contained some AChE activity; the significance of the presence of AChE in this fraction is discussed.

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.