Glycerophosphorylcholine Phosphocholine Phosphodiesterase Activity of Rat Brain Myelin

Myelin isolated from rat brain possessed the ability to release phosphorylcholine from glycerophosphorylcholine, and this activity was enriched 3.2-fold over that of the original homogenate. This glycerophosphorylcholine phosphocholine phosphodiesterase activity had a pH optimum at 9.5, had a Km of 0.2 mM, and a Vmax of 150 nmoles/mg protein/hr. The enzyme had a specific requirement for Zn+2 with an optimum concentration at 0.25 mM. Maximum enzyme activity was at 50 degrees C and an Arrhenius plot showed a breakpoint at 40 degrees. p-Nitrophenylphosphorylcholine was also hydrolyzed by purified myelin and was a competitive inhibitor of glycerophosphorylcholine phosphocholine phosphodiesterase activity with a Ki of 0.075 mM. Glycerolphosphorylethanolamine was hydrolyzed only 5% compared with GPC, but it was not an inhibitor.