Vitamin D-2 modulates melittin-membrane interactions

In the present work, mutual interaction of melittin, a pore forming hemolyt ic toxin from bee venom, and vitamin D-2, an antioxidant steroid, with dipa lmitoyl phosphatidylcholine (DPPC) multilamellar liposomes has been investi gated. Turbidity and Fourier transform infrared (FTIR) spectroscopic measur ements, in combination with thermodynamic calculations, were used to monito r the modulating effect of vitamin D-2 on a melittin-DPPC membrane system. The results indicate that melittin on its own decreases the main phase tran sition to lower temperatures and also dramatically decreases the stability of the membrane. It has an overall disordering effect on the phospholipid m embrane structures. Inclusion of vitamin D-2 at low concentrations (3, 6 mo l%) into melittin containing DPPC liposomes slightly shifts the main phase transition to lower temperatures. High concentration of vitamin D-2 (9 mol% ) has a more dramatic effect in shifting the main phase transition to lower temperature. It also causes a significant broadening in the phase transiti on curve. The present study also demonstrates that, with the addition of vi tamin D-2 into melittin-DPPC system, absorbance value in turbidity study an d the frequency of the CH, stretching band in FTIR study changes in a manne r that are consistent with a reduction in the membrane perturbing effect of melittin on DPPC liposomes. Vitamin D-2 diminishes the disordering effect of melittin on DPPC lipids and produces a more ordered membrane system. The se results were confirmed with thermodynamic calculations. (C) 2000 Elsevie r Science B.V. All rights reserved.