Effect of hydrophobic surfactant peptides SP-B and SP-C on binary phospholipid monolayers. I. Fluorescence and dark-field microscopy.
The influence of the hydrophobic proteins SP-B and SP-C, isolated from pulmonary surfactant, on the morphology of binary monomolecular lipid films containing phosphocholine and phosphoglycerol (DPPC and DPPG) at the air-water interface has been studied using epifluorescence and dark-field microscopy. In contrast to previously published studies, the monolayer experiments used the entire hydrophobic surfactant protein fraction (containing both the SP-B and SP-C peptides) at physiologically relevant concentrations (approximately 1 wt %). Even at such low levels, the SP-B/C peptides induce the formation of a new phase in the surface monolayer that is of lower intrinsic order than the liquid condensed (LC) phase that forms in the pure lipid mixture. This presumably leads to a higher structural flexibility of the surface monolayer at high lateral pressure. Variation of the subphase pH indicates that electrostatic interaction dominates the association of the SP-B/C peptides with the lipid monolayer. As evidenced from dark-field microscopy, monolayer material is excluded from the DPPC/DPPG surface film on compression and forms three-dimensional, surface-associated structures of micron dimensions. Such exclusion bodies formed only with SP-B/C peptides. This observation provides the first direct optical evidence for the squeeze-out of pulmonary surfactant material in situ at the air-water interface upon increasing monolayer surface pressures.
Krüger
P
P
Institute of Experimental Physics I, University of Leipzig, D-04103 Leipzig, Germany.
Schalke
M
M
Wang
Z
Z
Notter
R H
RH
Dluhy
R A
RA
Lösche
M
M
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000388:Air; D055592:Biophysical Phenomena; D001703:Biophysics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008563:Membrane Lipids / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011312:Pressure; D011510:Proteolipids / Q000737:chemistry* / Q000494:pharmacology*; D011650:Pulmonary Alveoli / Q000737:chemistry / Q000502:physiology; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000494:pharmacology*; D013499:Surface Properties; D014867:Water
D008563:Membrane Lipids; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; C030345:1,2-dipalmitoylphosphatidylglycerol