The action of ascorbate in vesicular systems.

Many effects of ascorbate center on its interactions with membranes from plant and animal cells. These actions can be studied using vesicles produced from phospholipid components (liposomes), by isolating naturally occurring vesicles, or by purifying particular membranes that form vesicles during the extraction process. Liposomes have provided information concerning the anti- and prooxidant properties of ascorbate and about how the water-soluble vitamin can have effects within the phospholipid bilayer. The involvement of ascorbate in transmembrane electron transport has been characterized in vesicles normally found in certain cells, such as, chromaffin granules, synaptosomes, glyoxisomes, peroxisomes, and clathrin-coated vesicles. Redox activity using reducing power associated with ascorbate/ascorbate free radical (AFR) has been characterized in some of these vesicles and it appears to be mediated by a b-type cytochrome. Ascorbate also participates in the reduction of iron within clathrin-coated vesicles. Vesicles appearing during purification of plasma membranes have transmembrane electron transport, oxidoreductase activity with ascorbate/AFR as redox agents, and an ascorbate-reducible b-type cytochrome. It is also possible that ascorbate-related redox activity exists at the tonoplast of plant cells.