Figure 4.

(a) Height difference and phase-contrast imaging of sPLA₂-induced membrane restructuring of the second bilayer in a supported double bilayer of a 1:1 DMPC/DSPC mixture visualized at 30°C. Before hydrolysis (−5 min), the membrane exhibits ripple (P_β′) domains, in coexistence with L_α-phase domains (20). As hydrolysis proceeds, a shrinkage in the fluid-phase regions and a broadening and collapse in the ripple structure is simultaneously observed, resulting in a flat L_β-phase membrane. Holes are seen to emerge after the hydrolytic burst. (b) The L_β-phase area fraction as a function of time after addition of sPLA₂. (c) Phase diagram and tie line indicating the fraction of L_β and L_α phase expected for the conditions in a. (d) Comparison between 1), the fraction of fluid-phase domains predicted by the tie line in c, 2), the area fraction of fluid-phase area measured by AFM, and 3), the area fraction of holes present in the image after the hydrolytic burst.