SURFACE-CHEMISTRY OF BINARY-MIXTURES OF PHOSPHOLIPIDS IN MONOLAYERS - INFRARED STUDIES OF SURFACE-COMPOSITION AT VARYING SURFACE PRESSURES IN A PULMONARY SURFACTANT MODEL SYSTEM

被引:31
作者
RANA, FR
MAUTONE, AJ
DLUHY, RA
机构
[1] UNIV GEORGIA, DEPT MED, ATHENS, GA 30602 USA
[2] UMDNJ, NEW JERSEY MED SCH, DEPT ANESTHESIOL, NEWARK, NJ 07103 USA
[3] UMDNJ, NEW JERSEY MED SCH, DEPT PHYSIOL, NEWARK, NJ 07103 USA
关键词
D O I
10.1021/bi00063a032
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Phospholipid monomolecular films at the air/water interface were studied using Langmuir-Blodgett (L-B) surface chemistry, P-31 NMR spectroscopy, and infrared (IR) spectroscopy. These monolayers were composed of binary mixtures of acyl chain perdeuterated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (i.e., DPPC-d62) with 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (i.e., DPPG). This particular PC-PG binary mixture was chosen for study since this lipid system has been used as a model for pulmonary surfactant, especially in conjunction with the so-called ''squeezing-out'' hypothesis of pulmonary mechanics. This theory predicts that upon successive compression-expansion cycles, a surfactant surface film will reorganize to exclude all components except DPPC, thus resulting in a stable, low surface tension film. Several general results were obtained from these experiments. First, we have developed a combined spectroscopic assay using high-resolution P-31 NMR spectroscopy in combination with the C-H and C-D vibrational intensities obtained from the IR spectroscopy of binary mixtures in which one component is acyl chain perdeuterated. Using attenuated total reflectance IR spectroscopy of transferred L-B films, this combined spectroscopic approach allows us to quantitatively describe the fractional composition of each component in the binary monomolecular film. Second, when these methods are applied to transferred monolayer films of DPPC-d62 and DPPG (at an initial PC:PG mole ratio of 7:1), we find no evidence for a ''squeezing-out'' of the DPPG monolayer component at high surface pressure resulting in an enrichment of the DPPC component in the transferred monolayer film. On the contrary, the IR results indicate that at high surface pressures, both DPPC-d62 and DPPG are ordered and oriented. IR integrated intensities show that the fractional composition of each component in the monolayer does not change with increasing surface pressure, even up to 70 mN m-1 on multiple cycles. These results do not support the so-called ''squeezing-out'' hypothesis of surfactant physiology, at least for this particular PC-PG binary mixture.
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页码:3169 / 3177
页数:9
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