A SPECIFIC RADIOISOTOPIC ASSAY FOR ACETYLCHOLINESTERASE AND PSEUDOCHOLINESTERASE IN BRAIN AND PLASMA

A radiometric procedure for assaying acetyl and pseudocholinesterase is presented. The method is based on the adsorption of unreacted substrates as their acid-1-14C choline esters on Amberlite CG-120 resin suspended in dioxane. The supernatant solution containing the product of hydrolysis, the free acid-1-14C, is counted in a liquid scintillation spectrometer. Blank values are less than 0.5% of the total radioactivity added initially and assays may be made with 0.01-1 mg of rat brain tissue or 0.01-1 μl of rat plasma. The method can be used for short or long term incubations. Rates of hydrolysis are presented for three substrates, Mecholyl, acetylcholine, butyrylcholine, with mouse, rat, guinea pig, rabbit, and bovine brain. Plasma values are given for rat and human plasma. Two specific inhibitors, BW 284C51 and iso-OMPA were shown to support the relative specificity of the procedure for acetylcholinesterase and pseudocholinesterase when specific substrates are employed. © 1969.