Hydrocarbon chain packing modes in lipids: effect of altered sub-cell dimensions and chain rotation
✍ Scribed by P.R. Maulik; M.J. Ruocco; G.G. Shipley
- Publisher
- Elsevier Science
- Year
- 1990
- Tongue
- English
- Weight
- 606 KB
- Volume
- 56
- Category
- Article
- ISSN
- 0009-3084
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✦ Synopsis
The lateral hydrocarbon chain packing modes of lipids have been described in terms of specific hydrocarbon sub-cells as deduced from single crystal structural studies. To understand the changes in hydrocarbon chain packing in lipid bilayers induced by variations in temperature, hydration, ion-binding, etc,, we have examined the effect on the calculated X-ray diffraction pattern of (a) systematic variations in the dimensions of the hydrocarbon sub-cell and (b) the effect of chain rotation at fixed lattice sites. For the O± (orthorhombic) sub-cell, the a and b sub-cell parameters were varied from a = 4.96 to 4.85/~ and b = 7.42 to 8.40 ./k in six steps and the positions (s = 2 sinO/~t) and intensities (I,~ = F 2) of the strong sub-cell reflections calculated. In this way, the conversion of the O± sub-cell (with either fixed chain orientations or simulated chain rotation) to the hexagonal (H) sub-cell (with chain rotation) was followed. Notably, the two strong reflections characteristic of the O 1 sub-cell at 4.12/~ (110) and 3.71 A (020) show progressive shifts in position and intensity, finally merging to give the strong (OIO) reflection at 4.2/~ characteristic of the hexagonal sub-cell. Similar calculations were performed for the orthorhombic (O'~) and monoclinic (Mr) sub-cells. This approach can be used to analyze changes in the X-ray diffraction data due to modifications of the hydrocarbon chain packing modes characteristic of simple and complex lipids.