PHOSPHOLIPASE A(2) IN HUMAN PLACENTAL SERUM

Intervillous blood was collected from term placentae at delivery, and sera were tested for phospholipase A(2) under various experimental con ditions. Enzyme activity was found to develop upon extended storage in the cold or at 37 degrees C. The enzyme is reversibly inhibited by di thiothreitol, requires Ca++ ions for activity, and tolerates various d etergents. The apparent molecular weight is 42 kDa. In all these param eters the serum enzyme behaves similar to the 42 kDa phospholipase A(2 ) which we recently purified to homogeneity from thoroughly washed pla cental tissue. Serum phospholipase A(2) appears to be generated by pro teolytic processing from a slightly larger inactive precursor which wa s detected immunochemically. Most likely this protein originates from fetal cells and may be released by membrane damage. We conclude that b oth placental serum and tissue harbour a novel type of phospholipase A (2) which is distinct from cytosolic and secretory phospholipases A(2) . Preference for arachidonate containing substrate suggests a role in eicosanoid production within gestational tissues. (C) 1997 by Elsevier Science Inc.