ACCESSIBILITY AND REACTIVITY OF ASCORBATE 6-PALMITATE BOUND TO ERYTHROCYTE-MEMBRANES

Lipophilic derivatives of ascorbic acid may protect lipid bilayers and micelles against lipid peroxidation. In this work the binding: access ibility, and reducing capacity of ascorbate 6-palmitate (A6P) were stu died in human erythrocyte membranes. In contrast to less lipophilic ca rbon-6-modified ascorbate derivatives, A6P bound to erythrocyte membra nes in a concentration-dependent manner. This binding was preserved fo llowing centrifugation washes, but was largely reversed by extraction with bovine serum albumin. Most of the ascorbyl groups of membrane-bou nd A6P were readily accessible to oxidation by water-soluble oxidants. Ferricyanide quantitatively oxidized membrane-bound A6P, but the latt er spared endogenous tocopherols from destruction. In EPR studies, A6P was much more effective than ascorbate in reducing nitroxide spin lab els positioned at either carbon-5 or carbon-16 of membrane-bound stear ic acid in both intact cells and in membranes. A6P, thus, appears to i ntercalate into the erythrocyte membrane with the ascorbyl group locat ed superficially, but with access to the hydrophobic membrane interior , and with the ability to recycle endogenous cu-tocopherol during oxid ant stress.