Release of GPI-anchored Zn2+-glycerophosphocholine cholinephosphodiesterase as an amphiphilic form from bovine brain membranes by bee venom phospholipase A2.

Abstract

Enzymatic release of Zn(2+)-glycerophosphocholine (GPC)cholinephosphodiesterase, as an amphiphilic form, from bovine brain membranes was examined. Of various membrane hydrolases, bee PLA2 was the most effective in the release of the GPC cholinephosphodiesterase (amphiphilic form, 63-70%) from membrane. Compared to pancreatic PLA2, bee PLA2 was more efficient in the release of GPC cholinephosphodiesterase. In pH-dependent release of GP1-anchored phosphodiesterase, there was a similar pH-release profile between PLA2-mediated release and spontaneous one, implying the involvement of membrane disruption in the PLA2 action. The PLA2-mediated release showed a limited time-dependence (until 45 min) and a limited dose dependence (up to 3 units/ml), characteristic of a receptor-type binding. An ionic binding of PLA2 to membrane may be alluded from the interfering effect of anionic phospholipids on the PLA2 action. In support of an interaction between PLA2 and membrane glycoproteins, the PLA2 action was found to be blocked by lectins, wheat germ agglutinin or concanavalin A. In combination with detergent, the PLA2-mediated release was found to be enhanced synergistically by saponin, a cholesterol-complexing agent. Meanwhile, an additive interaction between PLA2 and lysolecithin suggests that PLA2 action is independent of lysolecithin. It is suggested that the binding of PLA2 to specific sites of membranes, probably rich in GPI-anchored glycoproteins, may be related to the facilitated release of GPI-anchored proteins as amphiphilic form.