Identification, isolation, and partial characterization of a 7.5-kDa surfactant-associated protein

Human surfactant was analyzed for proteins associated with the lipids. Surfactant was isolated from lung lavage by the salt gradient centrifugation method, and the soluble proteins binding to the lipids were recovered by extraction with a low pH buffer. Antiserum to this preparation reacted with surfactant apoprotein A and a 7.5-kDa protein. The 7.5-kDa protein was isolated from reduced and alkylated lung lavage pellet by chromatography. The N-terminal amino acid sequence of the protein indicates that it is a novel protein.