Change of Catalytic Properties of Erythrocyte Acetylcholinesterase after Binding to Lecithin Liposomes

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Abstract
Phosphatidylcholine and phosphatidylserine + phosphatidylcholine liposomes were prepared with cholate and erythrocyte acetylcholinesterase (EC 3.1.1.7). Dipalmitoyllecithin- and egg lecithin-acetylcholinesterase complexes exhibit an affinity for acetylthiocholine different from that of the free enzyme. The binding to lecithin apparently abolishes the excess substrate inhibition of acetylcholinesterase; the affinity constants of acetylthiocholine, acetylcholine and acetylcarnitine for the lecithin-bound enzyme are higher than the ones found for the free enzyme. Binding to lecithin decreases the optimum pH value for acetylcholinesterase, increases the resistance of the enzyme to heat dénaturation and reduces the extent of activation by Ca^2+.