Purification and peptide mapping of rat brain choline acetyltransferase

Acetyl-CoA:choline O-acetyltransferase (EC 2.3.1.6) has been purified approximately 17,000-fold from rat brain. The purification protocol included acid and NH4SO4 precipitation, followed by chromatography on CM-Sephadex, phenyl-Sepharose, Sephadex G-150, and blue dextran Sepharose. Two peaks of enzyme activity were detected after blue dextran Sepharose chromatography containing an overall yield of approximately 4% of the starting enzyme activity. The final specific activity of the blue dextran fractions was 70 to 80 mumol of acetylcholine formed min-1 mg of protein-1. Sodium dodecyl sulfate electrophoresis of the blue dextran fractions revealed three closely spaced proteins with a molecular weight of approximately 67,000. Tryptic peptide maps were prepared for each of the gel bands and indicated that they contained nearly identical primary structure.