Phospholipase A2 (PLA2) activity in undifferentiated U937 cells.

PLA2 activity has been described in U937 cells. The present study characterized PLA2 activity in these undifferentiated cells. Cells were grown in suspension culture, harvested by centrifugation, and washed and homogenized in a neutral buffer containing standard proteinase inhibitors. A low speed supernatant was fractionated either by acid extraction or by sucrose density gradient centrifugation. PLA2 activity was measured using either L-alpha-1-palmitoyl-2-arachidonoyl[1-14C]-phosphatidylcholine or heat-inactivated [3H]oleic acid-labeled E. coli as substrates. Substrate-specific PLA2 activity was found in the acid-extracted and in the 25% sucrose fractions. Standard inhibitors were investigated with these PLA2 activities. Our results suggest undifferentiated U937 cells contain three distinct PLA2 activities. This is the first indication that more than one PLA2 activity is present in undifferentiated U937 cells.