Effect of hydrophobic surfactant proteins SP-B and SP-C on binary phospholipid monolayers: II. Infrared external reflectance-absorption spectroscopy |
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| Authors: | Brockman Jennifer M Wang Zhengdong Notter Robert H Dluhy Richard A |
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| Affiliation: | Department of Chemistry, University of Georgia, Athens 30602, USA. |
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| Abstract: | In situ external reflection infrared spectroscopy at the air-water interface was used to study the influence on phospholipid structure of an endogenous mixture of the two hydrophobic surfactant proteins, SP-B and SP-C, which are thought to play pivotal roles in the adsorption and function of pulmonary surfactant. Mixtures studied were 1:1, 2:1, and 7:1 (mol:mol) DPPC-d(62):DPPG, and 7:1 DPPC-d(62):DOPG, alone and in the presence of 0.5-10 wt % mixed SP-B/C purified chromatographically from calf lung surfactant extract. Perdeuteration of DPPC produced a shift in vibrational frequencies so that it could be differentiated spectroscopically from the phosphoglycerol component in the surface monolayer. CH(2) antisymmetric and symmetric stretching bands ( approximately 2920 and 2852 cm(-1)) along with the analogous CD(2) stretching bands ( approximately 2194 and 2089 cm(-1)) were analyzed, and band heights and peak wavenumber positions were assessed as a function of monolayer surface pressure. Small, near-physiological contents of 1-2 wt % SP-B/C typically produced the maximum observed spectroscopic effects, which were abolished at high protein contents of 10 wt %. Analysis of CH(2) and CD(2) stretching bands and C-H/C-D band height ratios indicated that SP-B/C affected PC and PG lipids differently within the surface monolayer. SP-B/C had preferential interactions with DPPG in 1:1, 2:1, and 7:1 DPPC-d(62):DPPG films that increased its acyl chain order. SP-B/C also interacted specifically with DOPG in 7:1 DPPC-d(62):DOPG monolayers, but in this case an increase in CH(2) band heights and peak wavenumber positions indicated a further disordering of the already fluid DOPG acyl chains. CD(2) band height and peak wavenumber analysis indicated that SP-B/C had no significant effect on the structure of DPPC-d(62) chains in 7:1 films with DPPG or DOPG, and had only a slight tendency to increase the acyl chain order in 1:1 films of DPPC-d(62):DPPG. SP-B/C had no significant effect on DPPC-d(62) structure in films with DOPG. Infrared results also indicated that interactions involving SP-B/C and lipids led to exclusion of PC and PG lipids from the compressed interfacial monolayer, in agreement with our previous report on the phase morphology of lipid monolayers containing 1 wt % SP-B/C. |
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| Keywords: | A/W, air-water DOPG, 12-dioleoyl-sn-glycero-3-phosphoglycerol DPPC, 12-dipalmitoyl-sn-glycero-3-phosphocholine. DPPC-d62, acyl chain perdeuterated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine DPPG, 12-dipalmitoyl-sn-glycero-3-phosphoglycerol LE, LCliquid expanded, liquid condensed monolayer phase PC, PGphophocholine, phosphoglycerol SP-B/C, column isolated bovine hydrophobic surfactant proteins SP-B and -C IRRAS, infrared external reflection-absorption spectroscopy |
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