The effect of magnesium ions on vitamin D-2-phospholipid model membrane interactions in the presence of different buffer media

Vitamin D plays important roles in the bone formation, in calcium and phosp horus homeostasis and in the treatment and prevention of many diseases. Ion s, especially divalent cations like Mg2+, have indispensable roles in many vital biological events. Mg2+ is involved in many fundamental processes suc h as stabilization of membranes and macromolecules, synthesis of nucleic ac id and proteins and formation and use of high-energy phosphate bonds. Mg2is also required for synthesis of more than 310 different enzymes of the bo dy and is, therefore, involved in many important activities. The roles of v itamin D and major ions in the body are quite well known. While there are s till many unresolved points about the exact molecular mechanism behind such diverse functions, in the present study, the interaction of Mg2+ with dipa lmitoyl phosphatidylcholine (DPPC) model membranes has been studied in the presence and absence of vitamin D, by using Fourier transform infrared (FTI R) spectroscopy and turbidity technique at 440 nm. The effect of different buffer media on the system has also been investigated. The temperature depe ndent investigation of the wavelength of the CH, antisymmetric stretching b ands revealed that, in the presence of N-[2-hydroxyethyl] piyerazine-N'-[2- ethanesulfonic acid] (Hepes) and phosphate buffer, addition of Mg2+ and/or vitamin D, into pure DPPC liposomes does not change the shape of the phase transition profile. Turbidity studies support these results. In the presenc e of Hepes buffer, the inclusion of Mg2+ and/or vitamin D, into pure DPPC l iposomes orders the system. In the presence of phosphate buffer, FTIR study showed that, addition of Mg2+ into pure DPPC liposomes disorders the syste m in the gel phase. The precipitation of Mg2+ with phosphates, which is pre sent in phosphate buffer, may be a reason for this difference in the effect . It is seen that, the binary mixture of Mg2+-DPPC and the ternary mixture of Mg2+-vitamin D-2-DPPC behave differently in the presence of two differen t buffer media. (C) 2000 Elsevier Science B.V. All rights reserved.