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

@entity845 @entity95 @entity1391 @entity141 @entity4095 @entity3634
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 @entity95 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 @entity845 symmetric stretching vibrational frequencies near 2850 cm-1. A broad gel-liquid crystal phase transition with an onset temperature of about 22 degrees C, and a completion temperature of about 38 degrees C was observed, with slight sample-to-sample variations in temperatures. A similar completion temperature was noted in DSC endotherms. @entity141 (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 @entity141 -induced phase separation caused by ion binding to @entity3634 and other acidic components. Evidence for a direct interaction between @entity141 and the @entity1391 groups was suggested through small @entity141 -induced shifts in the 1090 cm-1 symmetric @entity4095 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 @entity141 and protein in the spreading of surfactant. The power of FT-IR to acquire useful structural information from complex biological tissues is demonstrated.
