Enzymatic release of Zn2+-glycerophosphocholine cholinephosphodiesterase from brain membranes by glycosylphosphatidylinositol-specific phospholipases and its regulation.

Abstract

Enzymatic conversion of glycosylphosphatidylinositol (GPI)-linked Zn2+-glycerophosphocholine phosphodiesterase was investigated. The activity of glycosylphosphatidylinositol-specific phospholipase-D (GPI-PLD), based on the conversion of amphiphilic form of phosphodiesterase into hydrophilic form, showing an optimum pH of about pH 6.6, increased continuously until 60 min. The activity of membrane-bound GPI-PL, based on the formation of hydrophilic form of phosphodiesterase, exhibiting an optimum pH of 7.4, increased up to 30 min, and reached a plateau. Inhibition studies indicate that while GPI-PLD activity was generally sensitive to ionic bio-detergents, it was not inhibited by myristoyl glycerol, a neutral detergent. Meanwhile, the membrane-bound GPI-PL was not affected remarkably by these detergents except that myristoyl glycerol expressed a modest increase of activity of membrane bound GPI-PL. In addition, the membrane-bound GPI-PL appeared to be enhanced by by suramin or oleic acid, which strongly inhibited GPI-PLD. From this results, it is suggested that in brain there may be two phospholipases responsible for the conversion of membrane-bound GPI-anchors to hydrophilic forms, and that this conversion might be regulated by endogenous lipids.