Differential assay for choline acetyltransferase

Abstract A rapid and sensitive radiochemical assay for choline acetyltransferase (EC 2.3.1.6) is reported. The assay allows for the fact that during incubation of [ 14 C]acetyl-CoA and choline with a cell homogenate, at least one product is formed besides [ 14 C]acetylcholine, which passes an anion exchange column. In contrast to [ 14 C]acetylcholine, this major contaminant ([ 14 C]acetylcarnitine) is not hydrolyzed apparently by Electrophorus acetylcholinesterase. Therefore, two types of assays are performed, the one in the presence of an acetylcholinesterase inhibitor, the other in the presence of acetylcholinesterase from Electrophorus . After passing the reaction mixtures over anion exchange columns, the radioactivities of the effluents are determined. Their difference is proportional to the choline acetyltransferase activity.