The role of tightly bound phospholipid in the activity of erythrocyte acetylcholinesterase

Abstract

Acetylcholinesterase was extracted from bovine erythrocyte ghosts in a hypotonic (25 m0sm) phosphate buffer (pH 7.4) and solubilized with Lubrol WX (2 mg/ml). Solubilization resulted in a decrease of the partial specific volume of the acetylcholinesterase from 0.895 ml/g in the particulate fraction to 0.793 ml/g in the Lubrol WX solubilized fraction. Both the particulate fraction and the solubilized fractions gave Arrhenius plots with a discontinuity in the activation energy at 20°C. Phospholipase A2 or C did not abolish the discontinuity. Treatment with 1.77 M NaCl resulted in a linear Arrhenius plot of intermediate activation energy. The high salt treatment removed phospholipid not previously extracted by chloroform/methanol. The extracted phospholipid corresponded to cardiolipin on one and two dimensional silica gel chromatography. Addition of cardiolipin to a high salt-treated preparation of acetylcholinesterase restored the discontinuity in the Arrhenius plot. It is concluded that the physical state of cardiolipin, tightly bound to acetylcholinesterase by ionic interactions, modulates the catalytic activity of acetylcholinesterase.