Fourier transform infrared and differential scanning calorimetric studies of a surface-active material from rabbit lung

Alan J. Mautone, Kim E. Reilly, Richard Mendelsohn

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Abstract

A surface-active material with a chemical composition consistent with lung surfactant and with the ability to lower surface tension on a Wilhelmy balance to about 6 mN/m, has been isolated from rabbit pulmonary lavage. The thermotropic properties have been characterized with the techniques of Fourier transform infrared spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC). FT-IR melting curves were constructed from the temperature-dependence of the lipid CH2 symmetric stretching vibrational frequencies near 2850 cm-1. A broad gel-liquid crystal phase transition with an onset temperature of about 22°C, and a completion temperature of about 38°C was observed, with slight sample-to-sample variations in temperatures. A similar completion temperature was noted in DSC endotherms. Ca2+ (5-10 mM) increased the onset temperature of the lipid-melting event, and induced an ordering of surfactant and of its lipid extract at all temperatures studied. The effect on the lipids was suggestive of a Ca2+-induced phase separation caused by ion binding to phosphatidylglycerol and other acidic components. Evidence for a direct interaction between Ca2+ and the phosphate groups was suggested through small Ca2+-induced shifts in the 1090 cm-1 symmetric PO2 stretching frequency. Removal of most of the protein component from a 10:1 (lipid/protein, w/w) sample caused an ordering of the resultant lipid fractions. In contrast, removal of most of the protein component from a 20:1 sample resulted in no change in lipid order or thermotropic behavior. These observations are discussed in light of the roles played both by Ca2+ and protein in the spreading of surfactant. The power of FT-IR to acquire useful structural information from complex biological tissues is demonstrated.

Original languageEnglish (US)
Pages (from-to)1-10
Number of pages10
JournalBBA - Biomembranes
Volume896
Issue number1
DOIs
StatePublished - Jan 9 1987

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Biochemistry
  • Cell Biology

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