Detection and characterization of extracellular phospholipase A2 in pleural effusion of patients with tuberculosis

Extracellular phospholipase A2 activity has been identified in pleural fluid of patients with tuberculosis. This enzyme is a calcium requiring protein and has a pH optimum of 10.0. The enzyme was inhibited by the active site-directed histidine reagent, rho-bromophenacyl bromide. Ionic and non-ionic detergents, or the sulfhydryl reagent dithiothreitol, caused loss of enzyme activity. When substrate specificity was tested using 2-[1-14C]linoleoyl phospholipids as substrates, phosphatidyl-ethanolamine was the best substrate, followed by phosphatidylserine and phosphatidylcholine. This phospholipase A2 showed high affinity for heparin, and was recognized by a monoclonal antibody raised against phospholipase A2 from human synovial fluid. These findings suggest that an extracellular phospholipase A2, which may belong to the 14K group II phospholipase A2 family, exists in the pleural fluid of patients with tuberculosis.