AN FT-IR STUDY OF THE EFFECTS OF DISTEAROYLPHOSPHATIDYLGLYCEROL AND CYTOCHROME-C ON THE MOLECULAR-ORGANIZATION OF THE MONOOLEIN-WATER CUBICLIQUID-CRYSTALLINE PHASE

FI-IR spectroscopy was used to study changes in molecular organization of the cubic monoolein (MO)-H2O liquid-crystalline phase (70:30 wt%) upon introducing low amounts of cytochrome c (Cytc) and/or distearoylp hosphatidylglycerol (DSPG). The incorporation of DSPG into the lipid b ilayers increases the conformational order of acyl chains due to the d ecrease of the number of double-gauche conformers per chain. On the ot her hand, the entrapment of Cytc into the MO-DSPG-H2O phase causes the number of gauche-trans-gauche defects to decrease significantly. In t he MO-DSPG-H2O and MO-DSPG-Cytc-H2O phases, the OH groups of the MO gl ycerol residue possess higher mobility in comparison with the binary c ubic phase. At the same time, in the cubic phases, containing Cytc and /or 7 wt% of DSPG, the hydrogen bonding of the acyl chain carbonyl gro ups is clearly reduced. Analysis of the spectra in the region of water association band reveals that the hydrogen bonds of the entrapped wat er molecules are basically diminished as compared to the situation in pure water. In the MO-DSPG-H2O phase, water molecules participate in t he hydration of the PO2- group of DSPG, whereas the entrapment of Cytc eliminates this effect. As evident from the spectral characteristics of Cytc, the protein molecules retain their native secondary structure in the MO-DSPG-Cytc-H2O phase. The results presented are discussed on a basis of the lipid packing parameter concept. It is also suggested that the DSPG molecules in the lipid bilayer of the MO-DSPG-Cytc-H2O p hase are concentrated in the vicinity of the entrapped protein.