Pulmonary surfactant-associated proteins: their role in the expression of surface activity

Abstract

Pulmonary surfactant, obtained by differential centrifugation of canine lung wash, contained 7.4 .+-. 0.2% protein (wt/wt), primarily as a single entity with a MW of 35,000. Dispersions of natural surfactant or the lipid extracts of this material at a concentration of 20 mg/ml reduced the surface tension of a pulsating bubble to approximately 27 mN/m at maximum bubble radius (0.55 mm) and to 0 mN/m at minimum radius (0.4 mm). Surface activity of the lung wash surfactant was not affected by boiling, tryptic degradation or varying the H from 3.0 to 10.5. When compared on the basis of phospholipid concentration, no difference was observed in the surface tension profiles developed with varying amounts of natural surfactant or lipid extract. Amino acid analysis of acid hydrolysates revealed that the protein content of the lipid extracts was less than 0.009% (wt/wt), indicating that approximately 99.9% of the protein was removed during the extraction. An artificial preparation obtained from pure lipids reduces the surface tension of the pulsating bubble to 0 mN/m at minimum radius and 25 mN/m at maximum radius with a kinetic pattern similar to that observed with dispersions of lung wash surfactant or lipid extract. Apparently proteins associated with natural surfactant are not required for surfactant adsorption or the reduction of the surface tension.