The main phase transition temperatures (T_m) for dimyristoyl phosphatidylcholine (DMPC) and dipalmitoyl phosphatidylcholine (DPPC) were determined under pressure of various gases. The gases used are pure ones such as O_2, N_2, H_2, He, At, and mixed ones (air, 20.0% O_2 (He base), 10.1% N_2O (N_2 base) and 4.69% H_2 (N_2 base). The behaviors of the T_m by pressurization were classified into two groups. In the one group, T_m increased linearly with increasing pressure, while it decreased up to 10-20 MPa in the other group. The depression of the latter group comes from the large solubilities of the gases in water. Especially, the effect of nitrous oxide on the depression was marked and this suggests the strong influence of the action of dissolved gases on the frame of bilayer membranes.
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