False positiveness in a choline acetyltransferase assay caused by nonionic reducing reagents.

Dithiothreitol and 2-mercaptoethanol have been frequently used as protective agents of choline acetyltransferase (EC 2.3.1.6) during its purification. We found that those reagents reacted with acetyl-CoA to form products that were co-extracted with acetylcholine into organic scintillation liquid to be erroneously detected as high enzyme activity. An anionic reducing reagent, such as sodium thioglycolate, does not cause the above problem and can be an alternative protective agent.