DIFFERENTIAL SCANNING CALORIMETRIC STUDY OF THE EFFECT OF VITAMIN-D-3ON THE THERMOTROPIC PHASE-BEHAVIOR OF LIPIDS MODEL SYSTEMS

Differential scanning calorimetry has been used to investigate the eff ects of vitamin D-3 on the physical properties of model membranes incl uding pure phosphatidylcholines (PC's) of chain lengths from 14 to 18, pure dipalmitoylphosphatidylethanolamine (DPPE), and various mixtures of these lipids. The results demonstrate that the interactions of vit amin D-3 with PC's are dependent on acyl chain lengths. It was found t hat vitamin D, reduces the transition temperatures of PC's and PE's, b roadening the transition and reducing the enthalpy, eventually abolish ing the transition. The interaction of vitamin D-3 With PC varies with chain length; the transition of DMPC is abolished by only 15 mol% vit amin D-3 whereas 45 mol% vitamin D-3 is required to abolish the transi tion of DSPC. These variations in vitamin D-3 lipid interactions are f urther explored in various mixtures. In the mixture studies it is show n that vitamin D-3 affects the mixing properties of the lipids in the mixtures. The results suggest that the presence of vitamin D-3 in lipi ds can affect the lateral phase distributions of lipids, and thereby h ave important effects on membrane function.