THE AUTOXIDATION OF THIOL AMINO-ACIDS AND ASCORBATE AND THEIR COOPERATIVE EFFECTS AS ANTIOXIDANTS WITH TROLOX IN MICELLES AND LIPID BILAYERS

The thiols cysteine (1), homocysteine (2), acetylcysteine (3), glutath ione (4), and dithioerythritol (5) underwent autoxidation with control led rates of chain initiation (R(j)) when driven by azobis (2-amidino propane hydrochloride (ABAP). Cysteine exhibits the largest rate const ant. Thiols 2 and 4 inhibited the facile self-initiated autoxidation o f ascorbate and regenerated ascorbate from its oxidation product, dehy droascorbic acid. Thiols 1 and 2 inhibited ABAP - initiated peroxidati on of dilinoleoyl phosphatidylcholine (DLPC) membranes with a k(inh) s imilar to that of 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate ( Trolox). Thiols 1 - 4 all acted cooperatively with Trolox to inhibit A BAP-initiated peroxidation of DLPC membranes. Stoichiometric factors, n=0.31-0.63, are attributed to oxidative wasting reactions. Each thiol , 2, 4, and 5 when combined with ascorbate further extended the inhibi tion period mediated by Trolox during peroxidation of linoleate initia ted by lipid-soluble di-rert-butylhyponitrite (DBHN) in sodium dodecyl sulfate (SDS) micelles. The spin trap phenyl-tert-butylnitrone (PEN) exhibited only retardant (not antioxidant) activity during peroxidatio n of linoleate initiated by DBHN or ABAP in SDS micelles.