A MICROSOMAL MEMBRANE COMPONENT ASSOCIATED WITH IRON REDUCTION IN NADPH-SUPPORTED LIPID-PEROXIDATION

This study was conducted to determine whether a factor responsible for reduced nicotinamide adenine dinucleotide phosphate (NADPH)-supported lipid peroxidation in rat liver microsomes is involved in iron reduct ion by cooperation with NADPH-cytochrome P450 reductase. Under anaerob ic conditions, NADPH-dependent reduction of ferric pyrophosphate in mi crosomes was not dependent on cytochrome P450 levels and was not inhib ited by carbon monoxide (CO). All of the iron complexes with chelators such as adenosine 5'-diphosphate, pyrophosphate, nitrilotriacetate, o xalate or citrate were reduced in microsomes, although in the reconsti tuted system containing purified NADPH-cytochrome P450 reductase littl e or no iron reduction was found. A cytochrome P450-free fraction from a cholate-solubilized preparation of microsomes after passage through a laurate sepharose column was required for reduction of iron pyropho sphate in the reconstituted system leading to lipid peroxidation. The iron reduction was not inhibited by CO and was destroyed by heat treat ment or trypsin digestion of the fraction. All iron complexes were red uced in the presence of the fraction, using a reducing equivalent of N ADPH via NADPH-cytochrome P450 reductase. The results indicate that a heat-labile component, which is probably a protein distinct from cytoc hrome P450, is associated with iron reduction responsible for lipid pe roxidation in microsomes.