BIOCHEMICAL, PHYSIOLOGICAL AND MEDICAL ASPECTS OF UBIQUINONE FUNCTION

This presentation is a brief review of current knowledge concerning so me biochemical, physiological and medical aspects of the function of u biquinone (coenzyme Q) in mammalian organisms. In addition to its well -established function as a component of the mitochondrial respiratory chain, ubiquinone has in recent years acquired increasing attention wi th regard to its function in the reduced form (ubiquinol) as an antiox idant. Ubiquinone, partly in the reduced form, occurs in all cellular membranes as well as in blood serum and in serum lipoproteins. Ubiquin ol efficiently protects membrane phospholipids and serum low-density l ipoprotein from lipid peroxidation, and, as recent data indicate, also mitochondrial membrane proteins and DNA from free-radical induced oxi dative damage. These effects of ubiquinol are independent of those of exogenous antioxidants, such as vitamin E, although ubiquinol can also potentiate the effect of vitamin E by regenerating it from its oxidiz ed form. Tissue ubiquinone levels are regulated through the mevalonate pathway, increasing upon various forms of oxidative stress, and decre asing during aging. Drugs inhibiting inhibiting cholesterol biosynthes is via the mevalonate pathway may inhibit or stimulate ubiquinone bios ynthesis, depending on their site of action. Administration of ubiquin one as a dietary supplement seems to lead primarily to increased serum levels, which may account for most of the reported beneficial effects of ubiquinone intake in various instances of experimental and clinica l medicine.