Obtaining high-quality crystals for X-ray diffraction from membrane proteins has proven to be a difficult task. One recently presented method utilises the cubic phases formed by 1-monooleoyl-rac-glycerol (MO). Removing the proteins from their native environment requires the use of surfactants. One commonly used surfactant is n-octyl-beta-D-glucopyranoside (OG). Using NMR techniques and visual observations, the ternary phase diagram of MO/OG/(H2O)-H-2 was outlined at 25 degreesC. The preliminary data show that all phases present in the binary systems at this temperature are also found in the ternary. Further, at the OG-rich side, an additional phase that appears to be hexagonal occurs. Addition of minor amounts (approximate to1.5 wt/wt %) of OG converts the cubic phases of MO to a lamellar structure, while the OG-rich cubic phase is able to dissolve about 15 wt/wt % MO. OG in water forms a large micellar solution phase;. Increasing the MO concentration at constant water content leads to a series of two- and three-phase areas in which one or two phases are in equilibrium with almost pure water
