THE EFFECT OF Cl− ON CHOLINE ACETYLTRANSFERASE KINETIC PARAMETERS AND A PROPOSED ROLE FOR Cl− IN THE REGULATION OF ACETYLCHOLINE SYNTHESIS

Abstract

Abstract— Crude or purified rat brain choline acetyltransferase (ChAc) is activated by anions. Among anions, Cl− is the most effective and may promote an up to 60 fold increase in Vmax. In the absence of Cl−, at low ionic strength, acetylcholine (ACh) is a good ChAc inhibitor (Ki= 0.310 mm). The ACh inhibition becomes negligible when Cl− is increased to 145 mm (ACh Ki= 45 mm). These results are discussed in terms of regulation of ACh synthesis by nerve terminals. It is proposed that ChAc is part of a presynaptic membrane bound multienzymatic complex under direct control of the ion fluxes promoted by nerve impulses.