A NOVEL PHOSPHOLIPASE A(2) FROM HUMAN PLACENTA

A major soluble phospholipase A(2) of human term placenta was characte rized and purified about 15 000-fold to homogeneity. The apparent mole cular mass as determined in SDS/polyacrylamide gels is 42 kDa. The enz yme is inhibited by dithiothreitol indicating the presence of disulphi de bridges which are essential for activity. Studies with known phosph olipase A(2) inhibitors revealed no immediate relationship to either s ecretory or cytosolic phospholipases A(2). The placental enzyme prefer s liposomes of phosphatidylcholine and has a distinct preference for a rachidonic acid in the sn-2 position. It tolerates various detergents. Roughly 10 mu M Ca2+ is required for activity, but it cannot be repla ced by Mg2+ or Mn2+; Zn2+, Cu2+ and Fe3+ are inhibitory. In immunoblot s, the placental enzyme was not detected by two separate antisera spec ific for type-II phospholipases A(2) but reacted very weakly with anti sera directed against cytosolic phospholipase A(2). From these data we suggest that this enzyme is a novel form of phospholipase A(2) which may be involved in arachidonic acid mobilization both during the cours e of pregnancy and at parturition.