ENZYMATIC RELEASE OF ZN2-GLYCEROPHOSPHOCHOLINE CHOLINEPHOSPHODIESTERASE FROM BRAIN MEMBRANES BY GLYCOSYLPHOSPHATIDYLINOSITOL-SPECIFIC PHOSPHOLIPASES AND ITS REGULATION()

Enzymatic conversion of glycosylphosphatidylinositol (GPI)-linked Zn2-glycerophosphocholine phosphodiesterase was investigated. The activit y 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 con tinuously until 60 min. The activity of membrane-bound GPI-PL, based o n the formation of hydrophilic form of phosphodiesterase, exhibiting a n optimum pH of 7.4, increased up to 30 min, and reached a plateau. In hibition studies indicate that while GPI-PLD activity was generally se nsitive to ionic bio-detergents, it was not inhibited by myristoyl gly cerol, a neutal detergent. Meanwhile, the membrane-bound GPI-PL was no t affected remarkably by these detergents except that myristoyl glycer ol expressed a modest increase of activity of membrane bound GPI-PL. I n addition, the membrane-bound GPI-PL appeared to be enhanced by by su ramin or oleic acid, which strongly inhibited GPI-PLD. From this resul ts, it is suggested that in brain there may be two phospholipases resp onsible for the conversion of membrane-bound GPI-anchors to hydrophili c forms, and that this conversion might be regulated by endogenous lip ids.