MECHANISM OF THE BIPHASIC EFFECT OF ETHYLENEDIAMINETETRAACETATE ON LIPID-PEROXIDATION IN IRON-SUPPORTED AND RECONSTITUTED ENZYMATIC SYSTEM

The biphasic action of ethylenediaminetetraacetate (EDTA), depending o n its concentration, on lipid peroxidation was examined in an iron-sup ported and reconstituted enzymatic system. In the presence of NADPH-cy tochrome P450 reductase and NADPH, Fe3+-PPi or Fe3+-ADP, though not re ducible in the absence of EDTA, was markedly reduced with increasing c oncentration of EDTA. Lipid peroxidation, in the reconstituted system containing negatively charged liposomes, showed the maximal rate at 0. 5 molar ratio of EDTA/iron, but no peroxidation occurred in positively charged liposomes, suggesting production of a positively charged iron complex as the prooxidant. Isotachophoresis indicated production of n et-negative charge, EDTA-Fe3+-PPi complex, from Fe3+-PPi and EDTA at 1 .1 ratio of EDTA/iron. The complex quenched Fe2+-PPi-supported lipid p eroxidation. We suggest that EDTA-iron complexes of different charges are generated, depending on the amount of EDTA in the enzymatic system and, consequently, there is a switch between prooxidant and inhibitor y effect at some critical ratio of EDTA/iron.