A FUNCTION OF LUNG SURFACTANT PROTEIN SP-B

The primary function of lung surfactant is to form monolayers at the a lveolar interface capable of lowering the normal surface tension to ne ar zero. To accomplish this process, the surfactant must be capable of maintaining a coherent, tight y packed monolayer that avoids collapse during expiration. The Positively charged amino-terminal peptide SP-B 1-25 of lung surfactant-specific protein SP-B increases the collapse p ressure of an important component of lung surfactant, palmitic acid (P A), to nearly 70 millinewtons per meter. This alteration of the PA iso therms removes the driving force for ''squeeze-out'' of the fatty acid s from the primarily dipalmitoylphosphatidylcholine monolayers of lung surfactant. An uncharged mutant of SP-B1-25 induced little change in the isotherms, suggesting that a specific charge interaction between t he cationic peptide and the anionic lipid is responsible for the stabi lization. The effect of SP-B1-25 on fatty acid isotherms is remarkably similar to that of simple poly-cations, suggesting that such polymers might be useful as components of replacement surfactants for the trea tment of respiratory distress syndrome.