Small-angle neutron scattering (SANS) was used to investigate the stru
cture of mixed colloids of egg yolk phosphatidylcholine (EYPC) with th
e bile salt, cholylglycine (CG), in D2O as a function of pressure (P)
and temperature (T). At atmospheric pressure, the system forms an isot
ropic phase of mixed, single bilayer vesicles (SLVs). Increasing the e
xternal hydrostatic pressure brought about significant changes in part
icle morphology. At T = 25 degrees C, application of a pressure of 3.5
MPa resulted in collapse of the SLVs. A further increase in P, up to
51.8 MPa, resulted in a transition from a phase of ordered (stacked),
collapsed vesicles to one of stacked, ribbon-like particles. A similar
collapse of the vesicles was observed at a higher temperature (T = 37
degrees C) with increasing P, but at this temperature, no ribbon phas
e was found at the highest pressure explored.