ISOLATION AND CHARACTERIZATION OF LUNG SURFACTANT

Lung surfactant was isolated from canine tracheal washings by differential centrifugation, equilibrium gradient centrifugation, and flotation on sucrose solutions. The preparation exhibits all the usual physical properties of surfactant, including a large hysteresis loop with low minimum surface tension, bubble clicking, bubble stability, and resistance to antifoam. It is a mixture of lipids, not a lipoprotein or a lipopolysaccharide. The total protein and carbohydrate content is less than 3%. and removal of these minor amounts of non-lipid materials does not affect surface properties. Phosphatidyl choline, phosphatidyl ethanolamine, cholesterol, and triglycerides are the major components. Other workers have extraceted surface-active phospholipids from tracheal washings and whole lung homogenates by using organic solvents, which would denature lipoproteins. Since our isolation does not employ such drastic techniques but yields a product which is essentially free of protein and carbohydrate but retains the properties of surfactant, we conclude that native surfactant is a mixture of lipids. © 1969.