Pulmonary surfactant proteins SP-B and SP-C in spread monolayers at the air-water interface: III. Proteins SP-B plus SP-C with phospholipids in spread monolayers.
Spread binary monolayers of surfactant-associated proteins SP-B and SP-C were formed at the air-water interface. Surface pressure measurements showed no interactions between the hydrophobic proteins. The effects of a mixture of SP-B plus SP-C (2:1, w/w) on the properties of monolayers of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and DPPC:DPPG (7:3, mol:mol) were studied. During compression of ternary and quaternary films, containing less than 0.4 mol% or 5 weight% total protein, the proteins were not squeezed out and appeared to remain associated with the film until collapse at surface pressures of about 65-70 mN.m-1. At initial concentrations of total protein of about 0.9 mol% or 10 weight%, exclusion of protein-lipid complexes was observed at 40-50 mN.m-1. Larger amounts of phospholipid were removed by proteins from (SP-B:SP-C)/DPPG films than from (SP-B:SP-C)/DPPC ones. Separate squeeze-out of SP-B (or SP-B plus DPPC) at about 40 mN.m-1, followed by exclusion of SP-C (or SP-C plus DPPC) at about 50 mN.m-1, was observed in (SP-B:SP-C)/DPPC films. This led to a conclusion that there was independent behavior of SP-B and SP-C in (SP-B:SP-C)/DPPC monolayers. The quaternary (SP-B:SP-C)/(DPPC:DPPG) films showed qualitatively similar process of squeeze-out of the proteins. In the ternary mixtures of SP-B plus SP-C with DPPG separate exclusion of SP-B was not detected; rather, the data was consistent with exclusion of a (SP-B:SP-C)/DPPG complex at about 50 mN.m-1. The results imply possible interactions between SP-B and SP-C and the acidic phospholipid.
Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada.
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D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000388:Air; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D066298:In Vitro Techniques; D008567:Membranes, Artificial; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011312:Pressure; D011510:Proteolipids / Q000737:chemistry*; D011650:Pulmonary Alveoli / Q000737:chemistry; D011663:Pulmonary Surfactants / Q000737:chemistry*; D013499:Surface Properties; D013552:Swine; D014867:Water
D008567:Membranes, Artificial; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; C030345:1,2-dipalmitoylphosphatidylglycerol