BRAIN MYELIN-BOUND ZN2+-GLYCEROPHOSPHOCHOLINE CHOLINEPHOSPHODIESTERASE IS A GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED ENZYME OF 2 DIFFERENT MOLECULAR-FORMS

A Zn2+-GPC cholinephosphodiesterase activity, which is present more predominently in myelin than in microsome or cytosol, has been examined using rho-nitrophenylphosphocholine as a substrate. In the solubilization of enzyme activity from myelin membranes, lysolecithin was found to be more effective than Triton X-100 or deoxycholate. Especially, the myelin-bound phosphodiesterase was suggested to be a glycosylphosphatidyl-inositol-anchored protein, based on solubilization by B. cereus phospholipase C and Triton X-114 phase separation. Interestingly, it was found that while phospholipase C-solubilized enzyme, a hydrophilic protein, was associable with Concanavalin A column, detergent-solubilized amphiphilic form of enzyme was not. Either detergent extract or cytosol was observed to contain both amphiphilic form and hydrophilic one. In CM-sephadex chromatography, the soluble hydrophilic phosphodiesterase was observed to be separatable into two forms of enzyme. In comparative studies, both forms of phosphodiesterase showed much similarity in substrate specificity, optimum pH, Km value and Zn2+ requirement, although they differed in charge property and molecular weight.