DIFFERENTIAL INHIBITION OF SOLUBLE AND MEMBRANE-BOUND ACETYLCHOLINESTERASE FORMS FROM MOUSE-BRAIN BY CHOLINE ESTERS WITH AN ACYL MOIETY OF AN INTERMEDIATE SIZE

Differential inhibitions of soluble and membrane-bound acetylcholinesterase forms purified from mouse brain were examined by the comparison of kinetic constants such as a K-m value, a K-ss value (substrate inhibition constant), and IC50 values of active site-selective ligands including choline esters. Membrane-bound acetylcholinesterase form (solubilized only in the presence of detergent) showed lower K-m and K-ss values than soluble acetylcholinesterase form (easily solubilized without detergent). Edrophonium expressed a slightly but significantly (p < 0.01) higher inhibition of detergent-soluble acetylcholinesterase form than aqueous-soluble acetylcholinesterase form, while physostigmine inhibited both forms with a similar potency. A remarkable difference in inhibition was observed using choline esters; although choline esters with acyl chain of a short size (acetyl- to butyrylcholine) or a long size (heptanoyl- to decanoylcholine) showed a similar inhibitory potency for two forms of acetylcholinesterase, pentanoylcholine and hexanoylcholine inhibited more strongly aqueous-soluble acetylcholinesterase than detergent-soluble acetylcholinesterase. Thus, it is suggested that the two forms of AChE may be distinguished kinetically by pentanoyl- or hexanoylcholine.