Institution: | Department of Biochemistry, School of Medicine, Gunma University, Maebashi 371, Japan |
Abstract: | Purified NADPH cytochrome c reductase catalyzes the oxidation of NADPH in the presence of Fe3+, ADP and EDTA. EDTA in this system appears to elevate the redox potential of ferric ion and of its iron complex thereby facilitating the transfer of one electron from NADPH to tri-valent iron (more rapidly than superoxide is formed) through a flavin moiety in the reductase, but it diminishes the concentration of free iron to be required for phospholipid peroxidation. The reduction of Fe3+ by the xanthine-xanthine oxidase system is different from that manifested by the NADPH-NADPH cytochrome c reductase system in the manner in which the former is carried out in the main by Ostaggered2staggered? · generated by the substrate - O2 - enzyme interaction. Reduced iron, which is free in the solution, plays an important role for the initiation and propagation of the phospholipid peroxidation, monitored by malondialdehyde assay and light emission. In the xanthine-induced lipoxygenation system, the ·OH radical, probably produced from hydrogen peroxide by the action of Fe2+, is not involved in the initiation of the peroxidative cleavage of phospholipid in microsomal lipoprotein. |