Isoenzymes of soluble and membrane-bound acetylcholinesterase in bovine splanchnic nerve and adrenal medulla

Abstract

Centrifugation of homogenates of bovine splanchnic nerve trunks and adrenal medulla showed that 47% and 31%, respectively, of the acetylcholinesterase activity was not sedimentable. The possibility that the soluble acetylcholinesterase activity was derived artefactually from the membrane-bound form was excluded. Gel electrophoresis revealed that the soluble acetylcholinesterase activity in adrenal medulla was distributed between five isoenzymes, only one of which was found in the supernatant fraction of splanchnic nerve homogenates. Solubilization of the membranes of both tissues with Triton X-100 gave a single isoenzyme of acetylcholinesterase, common to both tissues, whose electrophoretic mobility was less than that of any of the soluble isoenzymes. Some of the properties of the soluble and membrane-bound isoenzymes of acetylcholinesterase of splanchnic nerve were compared: the Michaelis constants were identical, both isoenzymes sedimented to the same position as catalase (molecular mass 240000) in a density gradient, their mobilities varied in a parallel fashion upon electrophoresis in gels of different concentration. It was concluded that the higher electrophoretic mobility of the soluble isoenzyme was because it carried a greater charge than, but had a similar molecular mass to, the membrane-bound isoenzyme.