CONTRIBUTION OF TYPE-II PHOSPHOLIPASE A(2) TO IN-VITRO PHOSPHOLIPASE A(2) ENZYMATIC-ACTIVITY IN HUMAN TERM PLACENTA

Although phospholipase A(2) (PLA(2)) enzymatic activities have been im plicated in the regulation of phospholipid metabolism and eicosanoid f ormation in human gestational tissues, the role and contribution made by individual PLA(2) isozymes has not been established. The aim of thi s study, therefore, was to determine the contribution made by Type II PLA(2) to PLA(2) enzymatic activity present in human term placenta. Th e experimental paradigm used to establish the contribution made by Typ e II PLA(2) to total in vitro PLA(2) enzymatic activity present in pla cental extracts was to remove Type II PLA(2) by immunoaffinity extract ion and then to quantify residual PLA(2) enzymatic activity. Before im munoaffinity extraction, Type II PLA(2) immunoactivity and total PLA(2 ) enzymatic activity present in placental extracts averaged 28.0 +/- 1 0.0 ng/mg protein and 1040 +/- 367 pmol/h per mg protein (n=3) respect ively. Alter solid-phase immunoaffinity batch extraction of placental extracts, immunoreactive Type II PLA(2) was not detectable by ELISA, a nd PLA(2) enzymatic activity was decreased by 82 +/- 1% (P<0.001). Res idual (i.e. non-Type II) PLA(2) enzymatic activity was further charact erised by Western blot analysis and enzyme activity assay. The data ob tained are consistent with a contribution by both cytosolic PLA(2) and other secretory PLA(2) isozymes (i.e. non-Type II) to residual PLA(2) enzymatic activity. The results obtained in this study support the co nclusion that Type II PLA(2) is quantitatively the primary PLA(2) isoz yme that contributes to in vitro PLA(2) enzymatic activity present in extracts of human term placenta, accounting for at least 80% of total activity. These data further support the involvement of this extracell ularly active isozyme in the regulation of placental phospholipid meta bolism and eicosanoid formation during late gestation.