Lung surfactant proteins, SP-B and SP-C, alter the thermodynamic properties of phospholipid membranes: a differential calorimetry study.
The ability of the low molecular weight lung surfactant-associated proteins, SP-B and SP-C, to alter the thermotropic properties of synthetic multilamellar vesicles was tested using differential scanning calorimetry (DSC). The presence of either SP-B or SP-C in dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG) multilamellar vesicles broadened the DSC thermogram and reduced the enthalpy of transition in a concentration-dependent manner. With both proteins, the temperature at which the peak of the phase transition (Tm) was detected was shifted to a higher value. The increase in Tm caused by both proteins was greater with DPPG than DPPC. We have interpreted these results as implying the presence of a protein-perturbed domain of lipid. Both SP-B and SP-C were found to influence the surface activity of the phospholipids in a concentration-dependent fashion. We speculate that instability of lipid packing predicted to occur at protein-created lipid domain boundaries may be important for the expression of surface activity in pulmonary surfactant.
Shiffer
K
K
Cardiovascular Research Institute, University of California, San Francisco 94143.
Hawgood
S
S
Haagsman
H P
HP
Benson
B
B
Clements
J A
JA
Goerke
J
J
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000818:Animals; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004285:Dogs; D008081:Liposomes; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011510:Proteolipids / Q000737:chemistry*; D011663:Pulmonary Surfactants / Q000737:chemistry*; D013816:Thermodynamics
D008081:Liposomes; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine; C030345:1,2-dipalmitoylphosphatidylglycerol