Detection and Characterization of a Type IIA Secretory Phospholipase A₂ Inhibitory Protein in Human Amniotic Fluid

抄録

Two types of phospholipase A₂ (PLA₂) 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 (PLIP-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 A₂ (sPLA₂ type IIA) by PLIP-II occurred in a dose-dependent manner (IC₅₀ about 0.82 μM), and the effect was stronger on sPLA₂ IIA than on pancreatic sPLA₂ (IC₅₀ about 3.11 μM). The ratio of the inhibitions of the sPLA₂ IIA by PLIP-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.