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A rapid radiochemical method for the determination of choline acetyltransferase

RADIOCHEMICAL assays of choline acetyltransferase (ChAT) must be based on reproducible, rapid and specific procedures for isolating ACh from the incubation mixture. In our laboratory this has been achieved by isolating labelled ACh by liquid cation exchange using sodium tetraphenylboron (Kalignost) in ethyl butyl ketone (FONNUM, 1969a. b). In the present report I will show that this method can be simplified considerably by using the scintillation mixture as extraction solvent and carrying out the extraction directly in the scintillation vial. Labelled ACh can subsequently be determined by liquid scintillation counting at high efficiency in the biphasic aqueous: toluene scintillation solution mixture. The principle involved would be applicable to other radiochemical enzyme assays based on different forms of organic solvent extraction such as in methods for AChE (POTTER, 1967) and aromatic amino acid decarboxylase (BROCH & FONNUM, 1972). Particular attention has been paid to the possible interference of acetylcarnitine in the assay of ChAT and the effect of acetyl-CoA concentration on the ChAT activity.