Structural relationship between the two small hydrophobic apoproteins in bovine pulmonary surfactant.
Lipid extracts of bovine pulmonary surfactant contain two very hydrophobic surfactant-associated proteins (SP) designated SP-B (15 kDa nonreduced) and SP-C (3.5 kDa). These two low molecular weight apoproteins were delipidated and purified on silica SEP-PAK cartridges using various reagents. Dansylation studies revealed that the 15 kDa apoprotein has three N-termini: Phe, Leu and Ile, while the 3.5 kDa apoprotein has two N-termini: Leu and Ile. In either protein, only a very small amount of N-Ile is present. Quantitative N-terminal dansylation analysis of the 15 kDa protein indicated that Phe and Leu (plus Ile) are present in a 1:1 ratio. Carboxy-terminal analysis showed that the 15 kDa protein contains C-terminal Gly, and the 3.5 kDa protein contains C-terminal Leu. Gas-phase amino terminal sequencing of the 15 kDa protein revealed almost exclusively the Phe-polypeptide (SP-B). These results suggest that the 15 kDa apoprotein is not an oligomer of SP-B and SP-C. The reason that analysis of SP-B reveals N-terminal Leu and Ile by dansylation which cannot be confirmed by amino acid sequencing is not known.
Department of Obstetrics & Gynaecology, University of Western Ontario, London, Canada.
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D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D006023:Glycoproteins / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011510:Proteolipids / Q000302:isolation & purification*; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000302:isolation & purification*; D012997:Solvents
D006023:Glycoproteins; D011510:Proteolipids; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D012997:Solvents