  (200 words) Oxidation of unsaturated lipids is a fundamental process involved
in cell bioenergetics as well as in cell death. Using giant unilamellar
vesicles and a chlorin photosensitizer, we asymmetrically oxidized the outer or
inner monolayers of lipid membranes. We observed different shape transitions
such as oblate to prolate and budding, which are typical of membrane curvature
modifications. The asymmetry of the shape transitions is in accordance with a
lowered effective spontaneous curvature of the leaflet being targeted. We
interpret this effect as a decrease in the preferred area of the targeted
leaflet compared to the other, due to the secondary products of oxidation
(cleaved-lipids). Permeabilization of giant vesicles by light-induced oxidation
is observed after a lag and is characterized in relation with the
photosensitizer concentration. We interpret permeabilization as the opening of
a pore above a critical membrane tension, resulting from the budding of
vesicles. The evolution of photosensitized giant vesicle lysis tension was
measured and yields an estimation of the effective spontaneous curvature at
lysis. Additionally photo-oxidation was shown to be fusogenic.
