DIFFERING FEATURES OF PROTEINS IN MEMBRANES MAY RESULT IN ANTIOXIDANTOR PROOXIDANT ACTION - OPPOSITE EFFECTS ON LIPID-PEROXIDATION OF ALCOHOL-DEHYDROGENASE AND ALBUMIN IN LIPOSOMAL SYSTEMS

The influence of 3 thiol-containing compounds, bovine serum albumin (f atty acid free: BSA), glutathione (GSH) and yeast alcohol dehydrogenas e (YADH) on lipid peroxidation in multilamellar liposomes, prepared fr om ox-brain phospholipid, was investigated, Thiol-compounds were added either before liposome formation, or after liposome formation; and th eir effects compared to a positive control, Bovine serum albumin (BSA) , an acidic hydrophilic protein, displays a small, concentration depen dent, antioxidant effect when added to preformed liposomes, A much lar ger antioxidant effect was observed when the BSA was entrapped inside the liposome, by adding BSA just prior to liposome preparation, In con trast, a Zn2+ containing redox enzyme, YADH, a basic hydrophobic membr ane-associating protein, displays a large pro-oxidant effect at much l ower concentrations especially when entrapped inside the liposome, Thi s was observed also with GSH; but per mole of -SH, YADH was about 18 t imes as powerful a pro-oxidant perhaps because of structural changes t o the membrane, Oxidized glutathione and N-acetylcysteine were also pr o-oxidant (cysteine and cystine showed little effect), Formation of th iyl radicals may occur in the presence of iron ions with these pro-oxi dant sulphur-containing compounds, Partial protection against lipid pe roxidation was observed with EDTA, desferrioxamine and protoporphyrin (IX), potent iron-chelating agents.