SURFACE CHARGE OF CHOLINE ACETYLTRANSFERASE FROM DIFFERENT SPECIES

—The adsorption of partially purified choline acetyltransferase (ChAc) from cat, rat, guinea-pig and pigeon brains by the cation exchange resins, CM-Sephadex (C-50) and Amberlite CG-50 II, was studied at various pH values and ionic strengths. ChAc from cat and rat were more strongly adsorbed by cation exchangers and therefore have a stronger net positive surface charge than those from guinea pig and pigeon. Experiments showed that the difference in adsorption between these two groups of enzymes could not be explained by overloading of the resin, by competitive effect of other proteins present in the enzyme preparations or by the presence of any component suppressing the adsorption of ChAc in any of the enzyme preparations. The adsorption of ChAc by a cation exchanger is very similar to its binding to synaptosome membranes. The significance of the positive surface charge of ChAc in studies on the compartmentation of ChAc in synaptosomes is discussed.