REGULATION OF PHOSPHATIDIC-ACID PHOSPHOHYDROLASE ACTIVITY DURING STIMULATION OF HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Phosphatidic acid phosphohydrolase (PPH) activity was determined in human polymorphonuclear leukocytes (PMNs) by measuring the hydrolysis of [P-32]phosphatidic acid (PA) added to cell sonicates. Enzyme activity was localized primarily to a soluble fraction. Soluble and particulate activities required magnesium and were inhibited by calcium, N-ethylmaleimide, sphingosine, and propranolol. The activity in unstimulated PMNs was 0.64 +/- 0.11 nmol of PA hydrolyzed.mg protein-1.min-1 in particulate and 4.20 +/- 0.42 in soluble fractions. Stimulation of PMNs with 1-mu-M f-Met-Leu-Phe (FMLP) for 10 min caused a slight decrease in soluble activity and a small increase in the activity of particulate fractions. Preincubation with 10-mu-M cytochalasin B for 5 min before FMLP stimulation markedly enhanced both of these changes. The effect of FMLP plus cytochalasin B was rapid (< 10 s), whereas the calcium ionophore A23187 (1-mu-M) and phorbol myristate acetate (100 ng/ml) caused slower and smaller changes in enzyme activity. These results indicate that after chemoattractant stimulation; PPH activity decreases in the soluble fraction and increases in the particulate fraction suggesting that PPH may participate in signal transduction in the PMN.