Structure of SP-B/DPPC mixed films studied by neutron reflectometry.
The structures of films of pulmonary surfactant protein B (SP-B) and mixtures of SP-B and dipalmitoylphosphatidylcholine (DPPC) at the air/water interface have been studied by neutron reflectometry and Langmuir film balance methods. From the film balance studies, we observe that the isotherms of pure DPPC and SP-B/DPPC mixtures very nearly overlay one another at very high pressures, suggesting that the SP-B is being excluded from the film. The use of multiple contrasts with neutron reflectometry at a range of surface pressures has enabled the mixing and squeeze out of the DPPC and SP-B mixtures to be studied. We can identify the SP-B component of the interfacial structure and its position as a function of surface pressure. The mixtures are initially a homogeneous layer at low surface pressures. At higher surface pressures, the SP-B is squeezed out of the lipid layer into the subphase, with the first signs detected at 30 mN m(-1). At 50 mN m(-1), the subphase is almost completely excluded from the DPPC layer, with the SP-B content significantly reduced. Only a small amount of DPPC appears to be associated with the squeezed out SP-B.
Fullagar
W K
WK
School of Molecular and Microbial Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
Holt
S A
SA
Gentle
I R
IR
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008968:Molecular Conformation; D009501:Neutron Activation Analysis / Q000379:methods*; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry* / Q000648:ultrastructure*
D008051:Lipid Bilayers; D037701:Pulmonary Surfactant-Associated Protein B; D015060:1,2-Dipalmitoylphosphatidylcholine