TY - JOUR
T1 - Thermodynamic effects of the hydrophobic surfactant proteins on the early adsorption of pulmonary surfactant
AU - Schram, Vincent
AU - Hall, Stephen B.
N1 - Funding Information:
This work was supported by HL 03502 and 54209, the Whitaker Foundation, and the American Lung Association of Oregon. Page charges were provided in part by the friends and family of Vern McKee.
PY - 2001
Y1 - 2001
N2 - We determined the influence of the two hydrophobic proteins, SP-B and SP-C, on the thermodynamic barriers that limit adsorption of pulmonary surfactant to the air-water interface. We compared the temperature and concentration dependence of adsorption, measured by monitoring surface tension, between calf lung surfactant extract (CLSE) and the complete set of neutral and phospholipids (N&PL) without the proteins. Three stages generally characterized the various adsorption isotherms: an initial delay during which surface tension remained constant, a fall in surface tension at decreasing rates, and, for experiments that reached ∼40 mN/m, a late acceleration of the fall in surface tension to ∼25 mN/m. For the initial change in surface tension, the surfactant proteins accelerated adsorption for CLSE relative to N&PL by more than ten-fold, reducing the Gibbs free energy of transition (ΔG0‡) from 119 to 112 kJ/mole. For the lipids alone in N&PL, the enthalpy of transition (ΔH0‡, 54 kJ/mole) and entropy (-T · ΔS0‡, 65 kJ/mole at 37°C) made roughly equal contributions to ΔG0‡. The proteins in CLSE had little effect on -T · ΔS0‡, (68 kJ/mole), but lowered ΔG0‡ for CLSE by reducing ΔH0‡ (44 kJ/mole). Models of the detailed mechanisms by which the proteins facilitate adsorption must meet these thermodynamic constraints.
AB - We determined the influence of the two hydrophobic proteins, SP-B and SP-C, on the thermodynamic barriers that limit adsorption of pulmonary surfactant to the air-water interface. We compared the temperature and concentration dependence of adsorption, measured by monitoring surface tension, between calf lung surfactant extract (CLSE) and the complete set of neutral and phospholipids (N&PL) without the proteins. Three stages generally characterized the various adsorption isotherms: an initial delay during which surface tension remained constant, a fall in surface tension at decreasing rates, and, for experiments that reached ∼40 mN/m, a late acceleration of the fall in surface tension to ∼25 mN/m. For the initial change in surface tension, the surfactant proteins accelerated adsorption for CLSE relative to N&PL by more than ten-fold, reducing the Gibbs free energy of transition (ΔG0‡) from 119 to 112 kJ/mole. For the lipids alone in N&PL, the enthalpy of transition (ΔH0‡, 54 kJ/mole) and entropy (-T · ΔS0‡, 65 kJ/mole at 37°C) made roughly equal contributions to ΔG0‡. The proteins in CLSE had little effect on -T · ΔS0‡, (68 kJ/mole), but lowered ΔG0‡ for CLSE by reducing ΔH0‡ (44 kJ/mole). Models of the detailed mechanisms by which the proteins facilitate adsorption must meet these thermodynamic constraints.
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U2 - 10.1016/S0006-3495(01)75807-9
DO - 10.1016/S0006-3495(01)75807-9
M3 - Article
C2 - 11509366
AN - SCOPUS:0034872359
SN - 0006-3495
VL - 81
SP - 1536
EP - 1546
JO - Biophysical Journal
JF - Biophysical Journal
IS - 3
ER -