Biosynthesis of ubiquinone in the rat

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Abstract
The isoprenoid side chain of ubiquinone can by synthesized from acetate by each tissue of the rat in vivo. The rate of incorporation of [2-C14]-acetate into ubiquinone, however, is much slower than into cholesterol. Small but significant amounts of [2-C14]-mevalonate can be incorporated into ubiquinone by the everted intestinal sac in the presence of unlabelled ubiquinone supplements. A small quantity of aromatic nucleus is apparently available in the tissue under these conditions. The tissues of normal stock-colony rats contain mainly ubiquinone-45 with smaller amounts of the -50, -40 and -35 homologues in that descending order. The relative proportions in the liver are affected by dietary ubiquinones, which can be stored there temporarily. The administration of ubiqui-none-50, however, in amounts from 100 to 450 ug/rat/day did not affect the concentrations of ubiquinone-45 in liver and intestine, which tend to remain constant at about 130 and 32 [mu]g/g of tissue respectively. It appears therefore that the exogenous ubiquinone cannot exchange with or flush out the endogenous material which is in the mitochondria. It is presumably localized in another part of the cell and may therefore not be functional in the animal itself.