Changes of the behavior of the thermotropic phase transitions of the phospholipid DHPC by the action of miniprotein gramicidin D (G.D) have been studied by differential scanning calorimetry. The experimental results demonstrated that G.D could not remove the pretransition of DHPC, but the pretransition peak and the main transition peak of DHPC were incorporated into a broad peak. The pretransition temperature and the main transition temperature of DHPC decreased to different ex-tent. The sums of the pretransition and main transition enthalpies of DHPC showed a lineally decreasing relationship with increasing the mole fraction x_g of gramicidin D.
The effects of glucose and sucrose on the hydratd DHPE phase transitions have been studied by using differential scanning calorimetry. The experimental results demonstrated that the Lβ→Lα Phase transihon temperature increased lineary with increasing the concentration c of sugars. With glucose, there is a relationship T=344. 37 +0.916 c(correlation coefficient r=0. 994; with sucrose, T=344.39+1.841c(r=0.9996). The ability of sucrose to decrease the Lα→HⅡ Phase transihon temperatue was far stronger than that of glucose. In general, both glucose and sucrose could increase the cooperativity of Phase transition of hydraed DHPE, in addihon to influence the phase transihon enthalpies of hydraed DHPE. For the system of hydrated DHPE,both glucose and sucrose are kosmotropes, and they exert Hofmeister effect to influence the Phase transitions of hydraed DHPE. In comparison with glucose, sucrose should be quite a hopeful cryoprotectant in Preservation of phospholipid bilayers structure.
