Studies on phospholipase A inhibitor in blood plasma. I. Purification and characterization of phospholipase A inhibitor in bovine plasma.

Phospholipase A inhibitor was found in bovine, human and porcine plasma. The inhibitor was purified about 300-fold from bovine plasma by ammonium sulfate fractionation, DEAE-cellulose chromatography, Sephadex G-200 gel filtration and anti-BSA antibody-agarose column chromatography to remove albumin. The purified material was homogeneous as judged by immunoelectrophoresis and 0.7% agarose-2% polyacrylamide gel electrophoresis. The inhibitor suppressed not only rat and human plasma phospholipase A2 activity, but also purified Mamushi (Agkistrodon halys blomhoffi) venom phospholipase A2-II. Bovine plasma inhibitor was shown to be a lipoprotein containing phosphatidylcholine, sphingomyelin, cholesterol ester, and triacyl glycerol as major lipid components. The molecular weight of the native inhibitor was nearly the same as that of bovine plasma high density lipoprotein (HDL) when determined by the gel filtration method. The molecular weights of two subunits of the inhibitor observed on polyacrylamide gel electrophoresis in the presence of SDS were about 10K and 42K. The anti-inhibitor antiserum obtained from rabbits immunized with the highly purified inhibitor cross-reacted with bovine plasma alpha-lipoprotein (HDL). The lipid composition of the inhibitor was similar to that of HDL, but apoinhibitor and apoHDL were different in molecular weight and solubility in various buffers.