[Methodological study on the assay of glycosylphosphatidylinositol-specific phospholipase D activity in serum]

A method for the assay of glycosylphosphatidylinositol-specific phospholipase D(GPI-PLD) activity in human serum was established by using glycosylphosphatidylinositol(GPI) anchored placental alkaline phosphatase(PLAP) as a substrate. Serum GPI-PLD activity was determined both qualitatively and quantitatively by PEG/dextran and triton-X-114 partitioning respectively, and some kinetic properties of its enzymatic reaction were also studied. This method revealed a satisfactory reproductivity(CV = 3.6%) and a high sensitivity(2 microliters serum was sufficient). In addition, it is practical, economical, and feasible to be widely applied. The activities of GPI-PLD measured by this method in 100 normal subjects ranged from 30% to 50% (in terms of the percentage of converting GPI anchored PLAP substrate to the anchor-free product).