Water binding and phase structures for different Acholeplasma laidlawii membrane lipids studied by deuteron nuclear magnetic resonance and x-ray diffraction.

Water binding capability and phase structures for different lipid species extracted from Acholeplasma laidlawii A membranes have been studied using deuteron nuclear magnetic resonance and low-angle X-ray diffraction. The dominating membrane lipids are monoglucosyldiglyceride and diglucosyldiglyceride and each of them takes up limited amounts of water (bound plus trapped), i.e., up to 13% (w/w), whereas the phospholipids and phosphoglycolipids have larger hydration capacities. Addition of magnesium and calcium ions, but not sodium ions, to the diglucosyldiglyceride increases the hydration capability. This increase is accompanied by the formation of a metastable liquid crystalline phase and a hysteresis effect for the transition temperature. Large differences in water deuteron quadrupole splitting were observed between mono- and diglucosyldiglyceride. Both 2H nuclear magnetic resonance and low-angle X-ray diffraction studies on lipids containing biosynthetically incorporated omega-d3-palmitic acid clearly indicate the existence of a reverse hexagonal phase structure for the monoglucosyldiglyceride and lamellar structures for the diglucosyldiglyceride and the other membrane lipids. The low hydration capability of the large diglucosyldiglyceride polar head is discussed in terms of polar head configuration. Both mono- and diglucosyldiglyceride have several physical properties similar to those of phosphatidylethanolamine.