Surface analysis of lipid layers at air/water interfaces

Summary. --Monolayers of a protein ~-lactoglobulin (~L) and two lipids distearoylphosphatidylcholine (DSPC) and dimirystoylphosphatidylcholine (DMPC) on aqueous subphase containing Na § or Ca 2+ ions are studied. The spreading isotherms and the ATR-FTIR spectra of LB plurilayers transferred, allow to deduce that a-helix conformation of ~-lactoglobulin is the prevailing form. The study of bidimensional mixtures between ~L with DSPC and with DMPC shows that the components are incompatible at the W/A interface. PACS 68.35.Md -Surface energy; thermodynamic properties. PACS 01.30.Cc -Conference proceedings. -I n t r o d u c t i o n .Bidimensional systems of amphiphiles represent a useful model for biological membranes.In particular, mixed monolayers of proteins and lipids represent the single monolayer of natural membranes. Besides these monolayers are well defined either by thermodynamic quantities or by the investigation of the molecular distribution and energies, and therefore constitute a useful way to study the orientation and interaction in cellular bilayers.In previous works, mixed films of lipids and polipeptides and of different polipeptidic substances were studied [1].To improve the representativity of monolayer model, a study of mixed monolayers of a protein ~-lactoglobulin (~L) with phospholipids with different length of the hydrophobic chains is reported.

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“…The LB layers spectra obtained for DMPC and DSPC are close to that reported in the literature for L-a-dipalmitoylphosphatidylcholine (DPPC) [12].…”

Section: -E X P E R I M E N T a Lsupporting

confidence: 84%

“…Similar behaviour has been found for palmitic and stearic acid, in which cases the band at 1740cm -1, strong in solid-state spectra, completely disappeared in LB layers [12,13].…”

Section: -E X P E R I M E N T a Lsupporting

confidence: 82%

Monolayers of proteins: β-lactoglobulin and its interactions with phospholipids

et al. 1994

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“…Rana et al (1 993) examined monolayers of DPPC-d62/DPPG that had been transferred from the A/W interface to a Ge substrate and found no evidence for exclusion of the DPPG, in good accord with the current result. In an earlier study, Chung et al (1990) had examined mixed monolayers of egg PG (mixed saturated and unsaturated chains) with DPPC-daz. The authors concluded that squeeze out occurred, a result that Pastrana-Rios et al bulk phase morphology is the apearance of extensive domain structures in monomolecular phospholipid films.…”

Section: Discussionmentioning

confidence: 99%

A Direct Test of the "Squeeze-Out" Hypothesis of Lung Surfactant Function. External Reflection FT-IR at the Air/Wave Interface

Pastrana-Rios¹,

Flach²,

Brauner³

et al. 1994

Biochemistry

104

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The current theory of pulmonary surfactant function requires that very low surface tension be achieved and maintained in the alveolar surface film during compression (expiration). To effect this condition, it has been hypothesized that the unsaturated and/or fluid components of surfactant are selectively excluded or "squeezed out" from mixed monolayers containing both saturated and unsaturated phospholipids, leaving a surface film of essentially pure 1,2-dipalmitoylphosphatidylcholine (DPPC). External reflection Fourier transform infrared (FT-IR) spectroscopy has been employed to quantitatively test this hypothesis. Mixed monolayer films of acyl chain-perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC-d62) with 1,2-dioleoylphosphatidylglycerol (DOPG), 1-palmitoyl, 2-oleoylPG (POPG), 1,2-dipalmitoylPG (DPPG) were examined in situ at the air/water interface as a function of surface pressure. The relative intensities of CD2 (CH2) stretching vibrations of the deuterated (proteated) components permitted quantitative determination of the relative concentrations of each in the film. For 7:1 (mol:mol) mixtures of DPPC-d62/DOPG, progressive, selective squeeze out of up to about 90% of the PG component is observed over a range of surface pressures from about 51 to 68 mN/m. The extent of maximal PG squeeze out was reduced to 61% for a 7:1 (mol:mol) mixture of DPPC-d62/POPG. This phenomenon, which is at least partially reversible, appears to require relatively high rates of film compression. Squeeze out was reduced (< 20%) for 7:1 (mol:mol) mixtures of DPPC-d62/DPPG or for 7:3 mixtures of DPPC-d62/POPG. Squeeze out requires that the lipid mixture achieve surface pressures greater than about 50-60 mN/m along with unsaturation (or at least conformational disorder) in the acyl chains of the non-DPPC component.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…A film of DPPC and PA (68:8 w/w) did not display a coexistence region and began to collapse at 62 mN/m. At higher PA fractions, the film collapses at lower pressure, -45 mN/m for a 50:50 ratio w/w (11). A film containing DPPC, PA, and SP-B1-25 (68:8:3 ratio w/w) showed two distinct compressible phases.…”

mentioning

confidence: 99%

“…Lower collapse pressures lead to the ejection of these components from simple anionic lipid-DPPC mixed monolayers under sufficient compression. This effect has led to the belief that anionic lipids and fatty acids are also ejected from lung surfactant monolayers, a phenomenon that has been referred to as "squeeze-out" (10)(11)(12). However, in addition to DPPC, anionic phospholipids, and fatty acids, lung surfactant contains specific proteins.…”

mentioning

confidence: 99%

A Function of Lung Surfactant Protein SP-B

Longo

Bisagno

Zasadzinski

et al. 1993

Science

162

136

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The primary function of lung surfactant is to form monolayers at the alveolar interface capable of lowering the normal surface tension to near zero. To accomplish this process, the surfactant must be capable of maintaining a coherent, tightly packed monolayer that avoids collapse during expiration. The positively charged amino-terminal peptide SP-B1-25 of lung surfactant-specific protein SP-B increases the collapse pressure of an important component of lung surfactant, palmitic acid (PA), to nearly 70 millinewtons per meter. This alteration of the PA isotherms removes the driving force for "squeeze-out" of the fatty acids from the primarily dipalmitoylphosphatidylcholine monolayers of lung surfactant. An uncharged mutant of SP-B1-25 induced little change in the isotherms, suggesting that a specific charge interaction between the cationic peptide and the anionic lipid is responsible for the stabilization. The effect of SP-B1-25 on fatty acid isotherms is remarkably similar to that of simple poly-cations, suggesting that such polymers might be useful as components of replacement surfactants for the treatment of respiratory distress syndrome.

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Surface analysis of lipid layers at air/water interfaces

Cited by 24 publications

References 2 publications

Monolayers of proteins: β-lactoglobulin and its interactions with phospholipids

Monolayers of proteins: β-lactoglobulin and its interactions with phospholipids

A Direct Test of the "Squeeze-Out" Hypothesis of Lung Surfactant Function. External Reflection FT-IR at the Air/Wave Interface

A Function of Lung Surfactant Protein SP-B

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