Effects of a surfactant-associated protein and calcium ions on the structure and surface activity of lung surfactant lipids

Biochemistry. 1985 Jan 1;24(1):184-90. doi: 10.1021/bi00322a026.


Previous studies have demonstrated that lung-specific proteins are associated with surfactant lipids, particularly the highly surface active subfraction known as tubular myelin. We have isolated a surfactant-associated protein complex with molecular weight components of 36 000, 32 000, and 28 000 and reassembled it with protein-free lung surfactant lipids prepared as small unilamellar liposomes. The effects of divalent cations on the structure and surface activity of this protein-lipid mixture were investigated by following (1) the state of lipid dispersion by changes in turbidity and by electron microscopy and (2) the ability of the surfactant lipids to form a surface film from an aqueous subphase at 37 degrees C. The protein complex markedly increased the rate of Ca2+-induced surfactant-lipid aggregation. Electron microscopy demonstrated transformation of the small unilamellar liposomes (median diameter 440 A) into large aggregates. The threshold Ca2+ concentration required for rapid lipid aggregation was reduced from 13 to 0.5 mM by the protein complex. This protein-facilitated lipid aggregation did not occur if Mg2+ was the only divalent cation present. Similarly, 5 mM Ca2+ but not 5 mM Mg2+ improved the ability of the protein-lipid mixture to form a surface film at 37 degrees C. Extensive aggregation of the surfactant lipids without protein by 20 mM Ca2+ or 20 mM Mg2+ did not promote rapid surface film formation. These results add to the growing evidence that specific Ca2+-protein-lipid interactions are important in determining both the structure and function of extracellular lung surfactant fractions.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium / pharmacology*
  • Dogs
  • Edetic Acid / pharmacology
  • Kinetics
  • Liposomes
  • Lung / metabolism*
  • Microscopy, Electron
  • Phospholipids / isolation & purification
  • Phospholipids / metabolism*
  • Pressure
  • Proteins / isolation & purification
  • Proteins / metabolism*
  • Pulmonary Surfactants / isolation & purification
  • Pulmonary Surfactants / metabolism*
  • Surface Properties


  • Liposomes
  • Phospholipids
  • Proteins
  • Pulmonary Surfactants
  • Edetic Acid
  • Calcium