EFFECT OF CALCIUM ON PHOSPHOLIPID INTERACTION WITH PULMONARY SURFACTANT PROTEIN-C

Porcine pulmonary surfactant-associated protein SP-C was incorporated into bilayers of chain-perdeuterated dipalmitoylphosphatidylglycerol ( DPPG-d(62)) and chain-perdeuterated dipalmitoyl-phosphatidylcholine (D PPC-d(62)) and into bilayers containing 70 mol% dipalmitoyl-phosphatid ylcholine (DPPC) and 30 mol% DPPG-d(62) or 70 mol% DPPC-d(62) and 30 m ol% dipalmitoylphosphatidylglycerol (DPPG), The effect of SP-C on the phase behavior, lipid chain order, and dynamics in these bilayers was examined by using deuterium nuclear magnetic resonance. SP-C was found to have a similar effect on the chain order and phase behavior of DPP C-d(62) and DPPG-d(62) in bilayers with a single lipid component. In g el phase DPPC/DPPG (7:3) bilayers with one or the other lipid componen t chain-perdeuterated, SP-C was found to affect first spectral moment more strongly for DPPG-d(62) than for DPPC-d(62). This may indicate th at SP-C induced a nonrandom lateral distribution in the mixed lipid bi layer, SP-C was also found to influence motions responsible for deuter on transverse relaxation in both the gel and liquid crystalline phases , The presence of 5 mM Ca2+ in the aqueous phase substantially altered the effect of SP-C on transverse relaxation in the bilayer.