Type II phospholipase A2 in human gestational tissues: Subcellular distribution of placental immuno and catalytic activity

Abstract The aims of this study were to determine the Subcellular distribution of Type II phospholipase A 2 immunoactivity (irPLA 2 ) and in vitro net PLA 2 catalytic activity in human term placenta and to establish the efficacy of previously utilised homogenisation procedures with respect to the quantitative recovery of Type II PLA 2 immunoreactive and in vitro net PLA 2 catalytic activity. Type II PLA 2 immunoactivity and PLA 2 catalytic activity recovered in 900 × g supernates prepared from placental tissue ( n = 3) homogenised in low ionic strength media (sucrose 0.32 M Hepes 20 mM; phosphate-buffered saline or phosphate-buffered saline containing 3 mM EGTA) was less than 10% of that recovered following homogenisation in high ionic strength medium (ammonium sulphate 10%, w/v). The Subcellular distribution of Type II PLA 2 immunoactivity and PLA 2 catalytic activity was established by the differential centrifugation (10 000, 20 000 and 100 000 × g) of placental homogenates ( n = 3). Although Type II PLA 2 immunoactivity was equally distributed throughout the particulate Subcellular fractions examined, PLA 2 catalytic activity increased by comparison in 100 000 × g particulate material. This apparent dissociation between irType II PLA 2 and catalytic activity may indicate the presence of other types of PLA 2 in this fraction. The data obtained in this study indicate that previous studies which have utilised low ionic strength extractions of human gestational tissue to characterise PLA 2 catalytic activity and Subcellular distribution have largely excluded the contribution made by Type II PLA 2 . Consequently, much of the available published data on the role of PLA 2 in human parturition is inadequate. A reappraisal of this enzyme's contribution to the biochemical events associated with human pregnancy and labour is required.