Choline acetyltransferase. Purification procedure and factors affecting chromatographic properties and enzyme stability

Purified choline acetyltransferase had a specific activity of 142 mumol of acetylcholine produced min-1 mg-1 and consisted of two proteic forms with Mr = 72,000 and 76,000 on sodium dodecyl sulfate gel electrophoresis. The separation of more than one peak of enzyme activity on CM-cellulose chromatography was shown to reflect the interaction of choline acetyltransferase with other proteins rather than the resolution of different isoenzymes. Purified choline acetyltransferase exhibited a high degree of stability. Enzyme stability was greatly dependent upon the procedures used to reach a given degree of purity, rather than the degree of purity per se, suggesting that specific proteins may be involved in the mechanism of enzyme inactivation. Use of affinity chromatography over Sepharose-blue dextran early in the preparation produced enzyme which was unstable both to storage and to concentration. Although the addition of other proteins such as bovine serum albumin had no significant stabilizing effect, the presence of acetyl coenzyme A during concentration prevented inhibition. Finally, it was shown that the purified enzyme is representative of the total enzyme present in brain in terms of both specific activity and immunochemical properties.