The effect of components of rabbit pulmonary surfactant on the activity of phospholipases

This study investigates the ability of two components of pulmonary surfactant, protein and phosphatidylglycerol, to inhibit the action of phospholipases against phosphatidylcholine. Broncho-alveolar protein, prepared by de-lipidation of rabbit lung lavage material had an inhibitory effect on phospholipases A1 and A2 from rabbit lung lysosomes, comparable to the effect of bovine serum albumin. The degree of inhibition was found to increase with increasing enzyme activity. De-lipidated broncho-alveolar protein was separated into two fractions by gel chromatography. Inhibitory activity was associated only with the second peak, corresponding to rabbit albumin. The effect of phosphatidylglycerol (PG) on the activity of phospholipases A against dipalmitoyl phosphatidylcholine and unsaturated phosphatidylcholine (USPC) was investigated, and compared with the effects of two substrate analogues on the hydrolysis of USPC. There was no indication of true inhibition by PG, but some stimulation of USPC hydrolysis by 10 mol % PG. The relevance of these findings to the fate of surfactant in vivo is discussed.