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Mitochondrial Membrane Ghosts Produced by Lipid Peroxidation Induced by Ferrous Ion

II. COMPOSITION AND ENZYMATIC ACTIVITY

From the ¹ From the Edward Mallinckrodt Department of Pharmacology, Washington University School of Medicine, Saint Louis, Missouri 63110

Treatment of dilute suspensions of rat liver mitochondria with Fe²⁺ results in the formation of lipid peroxides, an extensive fall in turbidity, and the loss of 65% of the mitochondrial protein and 39% of the mitochondrial lipid into the suspending medium. These changes occur with little alteration in the number or size of the mitochondrial particles. The formation of mitochondrial membrane ghosts is suggested.

Membrane ghosts prepared from mitochondrial by Fe²⁺-induced peroxidation are found to retain almost no pyridine nucleotides, 33% of the total flavin, 50% of the ubiquinone, and 66%, 60%, and 27%, respectively, of the cytochromes a, b, and c + c₁ of the mitochondria. An additional 67% of the initial cytochrome c + c₁ is recovered from the supernatant medium following removal of the membrane ghosts by centrifugation.

The membrane ghosts rapidly oxidize succinate, glutamate, and 3-hydroxybutyrate in the presence of added nicotinamide adenine dinucleotide and cytochrome c. They show an antimycin A-insensitive NADH-cytochrome c reductase activity.

Fe²⁺-induced lipid peroxidation results in inactivation of all of the mitochondrial isocitrate dehydrogenase activity, 80% of the 3-hydroxybutyrate dehydrogenase, 36% of the malate dehydrogenase, and 23% of the succinate dehydrogenase. There is no loss of glutamate dehydrogenase activity. However, 96% of the glutamate dehydrogenase and 57% of the malate dehydrogenase are released into the soluble fraction.

Membrane ghosts prepared with Fe²⁺ exhibit no respiratory control or coupled phosphorylation with any of the substrates tested. There is an active Mg²⁺-dependent adenosine triphosphatase which is not stimulated by the addition of 2,4-dinitrophenol.

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