Phospholipase A activities in rat placentas of 14 days' gestation

1. Homogenates and subcellular fractions of placentas obtained from rats on the 14th day of gestation were assayed for enzymes characteristic of various subcellular organelles. Based on these assays it seemed the placental lysosomes (acid phosphatase activity) were distributed equally among the subcellular particulate fractions and that the cytosol was not contaminated by mitochondria or microsomes. 2. The placental preparations were assayed for phospholipase A activity using 2-[14-C] phosphatidylethanolamine. We found phospholipases A with pH optima of 4.0, 7.0, and 8.5. These enzymes had Ca-2+ requirements and subcellular localizations similar to those reported for adult rat liver (Waite, M., Scherphof, G.L., Boshouivers, F.M.G. and van Deenen, L.L.M. (1969) J. Lipid Res. 10, 411.) 3. The majority of the placental phospholipase A activity was found in the cytosol. We think this activity represents enzyme(s) solubilized from the plasma membranes of placental cells and speculate that this enzyme may be active in a placental transport mechanism.