Detection and characterization of a type IIA secretory phospholipase A2 inhibitory protein in human amniotic fluid

lTwo types of phospholipase A, (PLA,) inhibitory protein (PLIP-I, PLIP-II) were detected and isolated from human amniotic fluid by Sephacryl S300 gel filtration chromatography: The lower molecular weight-fraction (FLIP-II) was further purified by Sephadex G75 gel filtration and analyzed by SDS-PAGE, Its molecular weight was estimated to be approximately 18 kDa, and it was sensitive to heat treatment. Inhibition of phospholipase A(2) (sPLA(2) type IIA) by PLIP-II occurred in a dose-dependent manner (IC50 about 0.82 mu M), and the effect was stronger on sPLA(2) IIA than on pancreatic sPLA(2) (IC50 about 3.11 mu M). The ratio of the inhibitions of the sPLA(2) IIA by FLIP-II remained consistent over an entire range of substrate concentrations. Furthermore, addition of excess Ca2+ at concentrations of up to 10 mM did not antagonize the inhibitory activity of PLIP-II.