ROLE OF THE PALMITOYLATION OF SURFACTANT-ASSOCIATED PROTEIN-C IN SURFACTANT FILM FORMATION AND STABILITY

The effect of palmitoylation of pulmonary surfactant-associated protei n C (SP-C) on the surface activity of phospholipid mixtures of dipalmi toylphosphatidylcholine and phosphatidylglycerol was studied. Phosphol ipids reconstituted with palmitoylated or depalmitoylated bovine SP-C were examined at neutral and acidic pH using a captive bubble surfacto meter. At low pH, effective lipid adsorption and near zero surface ten sions upon compression were obtained even with protein-free samples, A t physiological pH, only SP-C-containing samples achieved such propert ies. Lipid adsorption was decreased by prior SP-C depalmitoylation. Bu bbles with palmitoylated SP-C were more mechanically stable and requir ed less compression to reach low surface tensions. Subphase depletion experiments showed that dynamically cycled surface layers containing p almitoylated SP-C maintained their surface activity after subphase lip id depletion. In contrast, surface activity was rapidly lost where dep almitoylated SP-C or SP-B tvas included. Our results indicate that alt hough SP-C palmitoylation has little effect on its ability to enhance lipid adsorption and surface tension reduction, it greatly enhances li pid respreading and film stability and is therefore important for surf actant function.