Solubilizaiton of the choline transport system and re-incorporation into artificial membranes.

The carrier-mediated transport of choline has been described in several types of cell and at isolated synaptic terminals. The operation of the caarrier seems to be a rate-controlling factor for the synthesis of acetylcholine at the synaptic terminals that release this neurotransmitter. The molecular mechanism by which the carrier transports choline is unknown and difficult to investigate because at present it can only be studied in the complex environment of the natural membrane in which it is situated. Furthermore, such studies are hampered by the results of metabolic activity inside the cell itself. The resolution of these difficulties by the separation, purification and examination of carriers in defined systems is hindered by the problem of assaying its activity during the purification procedure. We describe here the separation of the choline carrier from the membrane and its re-incorporation into unilamellar liposomes with retention of its functional activity, thus enabling its purification and examination in isolation to be undertaken.