Reduced Triphosphopyridine Nucleotide Oxidase-catalyzed Alterations of Membrane Phospholipids

Abstract

Fe3+ was shown to be required for enzyme-catalyzed peroxidative chain-scission of polyunsaturated fatty acids of phospholipids in liver microsomal membranes.The K, value for iron in the reaction is different from that of nonenzymic processes which cause similar alterations of phospholipids.The products of both reactions include malondialdehyde which was shown to be the only substance formed which reacts with thiobarbituric acid to form a pigment absorbing at 532 rnp.The enzymic reaction proceeds first through the formation of peroxides on the j?3 position polyunsaturated fatty acids followed by cleavage of the carbon chain to yield cat-bony1 compounds.Iron was shown to be required for formation of the phospholipid peroxides.The activity of the enzymic system in microsomes could be reduced to low levels by washing the particles several times in iron-free media.Activity could be restored by addition of Fe3f to the assay system.The results suggest that TPNH-dependent oxidation processes may contribute to the normal catabolism of phospholipids in microsomal membranes.