Isolation of apoprotein from bovine lung surfactant material by sodium deoxycholate

Aqueous solutions of bovine lung surfactant material were solubilized with a high concentration of sodium deoxycholate and the protein moiety could then be separated from the mixed lipid-sodium deoxycholate micelles by gel filtration in the presence of a micellar concentration of sodium deoxycholate of 10 mM. The lipid-free protein showed only one detectable peak in the gel filtrate and the sedimentation rate of this protein was 12.1 S. Sodium dodecyl sulfate disc gel electrophoresis showed essentially the same pattern as did the protein extracted directly from the bovine lung surfactant material with organic solvents, of which the major component has a molecular weight of 36 000. This protein should be the main apoprotein of lung surfactant material, and the main band in the sodium dodecyl sulfate disc gel electrophoresis, with a molecular weight of 36 000, would constitute the major protein subunit.