Conversion of glycosylphosphatidylinositol (GPI)-anchored alkaline phosphatase by GPI-PLD

Enzymatic conversion of brain glycosylphosphatidylinositol-linked alkaline phosphatase (GPI-AP), amphiphilic, was examined. When GPI-AP was incubated with glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD), a neg ligible conversion of GPI-AP to hydrophilic form was observed. The inclusio n of monoacylglycerols enhanced the enzymatic conversion, although the acti on of monoacylglycerols differed greatly according to the size of acyl grou p; the enzymatic conversion was enhanced considerably in the presence of mo noacylglycerols possessing acyl group of longer chain length (C-10.C-18), w hile monoacylglycerols with acyl moiety of shorter length (C-4-C-8) did fai l to augment the enzymatic conversion. Noteworthy, monooleoylglycerol was m uch more effective than the other monoacylglycerols in promoting the enzyma tic conversion, indicating a beneficial role of the unsaturation in acyl ch ain. Meanwhile, ionic amphiphiles such as monohexadecyllysophosphatidylchol ine and palmitoyl-carnitine decreased the enzymatic conversion of CPI-AP in a concentration-dependent manner, with monohexadecyllysophosphatidylcholin e being more inhibitory than palmitoylcarnitine. Separately, when CPI-AP wa s exposed to various oxidants prior to the incubation with GPI-PLD, a remar kable decrease of the enzymatic conversion was observed with hypochlorite a nd peroxynitrite generators, but not H2O2 In further study, hypochlorite wa s found to inactivate GPI-PLD at low concentrations (3 similar to 100 mu M) . From these results, it is suggested that the enzymatic conversion of GPI- AP by GPI-PLD may be regulated in vivo system.