INTERRELATIONSHIP BETWEEN VITAMIN E AND LIPIDE COFACTOR IN THE CYTOCHROME C REDUCTASE SYSTEM

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Abstract
By using large quantities of particulate cytochrome c reductase prepared from rat skeletal muscle and bovine heart muscle, it was shown that the crude lipid residue obtained by iso-octane-extraction of the enzyme contains vitamin E, most of it as a presumed tocopheryl quinone. Iso-octane removes only 10-20% of the total vitamin E, with a concomitant loss of 90% of the cytochrome c reductase activity. The amount of vitamin E extracted, however, cannot account for enzyme reactivation by added crude lipid residue. Instead, restoration is attributed to a lipid cofactor tentatively identified as a mixed triglyceride with stearate, palmitate, and oleate components. It is possible, however, that the small quantity of vitamin E removed by iso-octaine extraction may originally have been effective at the "active enzyme sites." The fact that the lipid cofactor and other active lipids potentiate the extractability of endogenous vitamin E suggests that they are acting by releasing the vitamin to the "active sites" of the enzyme. Whether the vitamin is functioning directly in electron transfer or indirectly as a binding substance remains to be established.