Generation of hydroxyl radicals during the enzymatic reductions of the Fe3+-ADP-phosphate-adriamycin and Fe3+-ADP-EDTA systems. Less involvement of hydroxyl radical and a great importance of proposed perferryl ion complexes in lipid peroxidation.

A system which contains NADPH, purified cytochrome P-450 reductase (enzyme) and Fe3+-ADP-adriamycin complex in Tris-HCl buffer does not produce hydroxyl radical, but possesses a strong lipid peroxidation activity on exogenously added phospholipid micelles. Fe3+-ADP-adriamycin complex, a tightly coordinated complex in Tris-HCl buffer, could be dissociated to Fe3+-ADP-phosphate complex and adriamycin in phosphate buffer. Hydroxyl radical, which can be detected by a spin trapping method using N-tert-butyl-alpha-phenylnitrone, is produced during the enzymatic reduction of a mixture of Fe3+-ADP-phosphate complex and adriamycin or of Fe3+-ADP-EDTA complex while it is not involved in phospholipid peroxidation under the conditions used. With hydroxyl radical-generating systems, little or no quenching of hydroxyl radical in Tris-HCl buffer could be demonstrated. The oxidative cleavage of phospholipid is initiated by the proposed perferryl ion complex, which may be generated by the interaction of Fe2+-ADP-adriamycin complex with O2. A similar perferryl ion complex is also produced during the enzymatic reduction of Fe3+-ADP-EDTA complex with a molar ratio of 2 for [Fe3+]/[EDTA] in the presence of air. This is also able to catalyze lipid peroxidation.