DYNAMICS OF XANTHINE OXIDASE-DEPENDENT AND FE3-ADP-DEPENDENT LIPID-PEROXIDATION IN NEGATIVELY CHARGED PHOSPHOLIPID-VESICLES()

Superoxide (O-2(-))-dependent lipid peroxidation on addition of xanthi ne oxidase (XO) and Fe3+-ADP was induced in egg phosphatidylcholine (P C) liposomes containing dicetylphosphate (DCP), which are negatively c harged like biological membranes, but not in uncharged egg PC liposome s, Positively charged Fe3+ ADP interacted more with negatively charged egg PC-DCP liposomes than with uncharged egg PC liposomes. The activi ties of Fe3+-chelates for initiating O-2(-)-dependent lipid peroxidati on were in the order Fe3+-ADP > Fe3+-citrate > Fe3+-oxalate = Fe3+-mal onate > Fe3+-EDTA = 0. This order was the same as that for the reducti on rates of these Fe3+-chelates to Fe2+-chelates by O-2(-)-generated b y XO. Lineweaver-Burk plots showed that the chelators inhibited XO by different mechanisms: uncompetitively by ADP and adenosine and noncomp etitively by organic acid chelators (citrate and oxalate) and EDTA, Th ese results suggest that ADP interacts with XO in a manner different f rom the other chelators, Lipid peroxidation by XO-xanthine and Fe3+-AD P was induced in egg PC liposomes containing a trace (0.31-0.35 mol%) of peroxidized egg PC (PC-OOH), but not in PC-OOH-free liposomes of eg g PC obtained by their pretreatment with triphenylphosphine. PC-OOH in corporated into dimyristoyl phosphatidylcholine (DMPC) liposomes was d egraded on addition of both XO-xanthine and Fe3+-chelate, but not of e ither one alone, alpha-Tocopherol in DMPC liposomes was oxidized on ad dition of XO-xanthine and Fe3+-chelates in the presence, but not in th e absence of PC-OOH, Furthermore, PC-OOH was required for decrease of the ESR spectrum of the spin probe 12-(N-oxyl-4,4'-dimethyloxazolidin- 2-yl)stearic acid, which labels the hydrophobic region of egg PC lipos ome membranes, on addition of XO-xanthine and Fe3+-chelates. These res ults indicate that the ''induction message of lipid peroxidation,'' wh ich is associated with reduction of Fe3+ ADP by O-2(-) and concurrent degradation of PC-OOH, must be transferred from the membrane surface t o the inner hydrophobic region of the membranes, (C) 1995 Academic Pre ss, Inc.