AN FT-IR STUDY OF THE EFFECTS OF DISTEAROYLPHOSPHATIDYLGLYCEROL AND CYTOCHROME-C ON THE MOLECULAR-ORGANIZATION OF THE MONOOLEIN-WATER CUBICLIQUID-CRYSTALLINE PHASE
V. Razumas et al., AN FT-IR STUDY OF THE EFFECTS OF DISTEAROYLPHOSPHATIDYLGLYCEROL AND CYTOCHROME-C ON THE MOLECULAR-ORGANIZATION OF THE MONOOLEIN-WATER CUBICLIQUID-CRYSTALLINE PHASE, Vibrational spectroscopy, 15(1), 1997, pp. 91-101
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.