Coenzima Q10

http://www.jacn.org/content/20/6/591.long

Biochemical Functions of Coenzyme Q10
Frederick L. Crane, PhD
- Author Affiliations

Department of Biological Sciences, Purdue University, West Lafayette, Indiana
Address correspondence to: Frederick L. Crane, Ph D, Department of Biological Sciences, Purdue University, West Lafayette, Indiana.
Next SectionAbstract
Coenzyme Q is well defined asa crucial component of the oxidative phosphorylation process in mitochondria which converts the energy in carbohydrates and fatty acids into ATP to drive cellular machinery and synthesis. New roles for coenzyme Q in other cellular functions are only becoming recognized. The new aspects have developed from the recognition that coenzyme Q can undergo oxidation/reduction reactions in other cellmembranes such as lysosomes, Golgi or plasma membranes. In mitochondria and lysosomes, coenzyme Q undergoes reduction/oxidation cycles during which it transfers protons across the membrane to form a proton gradient. The presence of high concentrations of quinol in all membranes provides a basis for antioxidant action either by direct reaction with radicals or by regeneration of tocopherol andascorbate. Evidence for a function in redox control of cell signaling and gene expression is developing from studies on coenzyme Q stimulation of cell growth, inhibition of apoptosis, control of thiol groups, formation of hydrogen peroxide and control of membrane channels. Deficiency of coenzyme Q has been described based on failure of biosynthesis caused by gene mutation, inhibition of biosynthesis byHMG coA reductase inhibitors (statins) or for unknown reasons in ageing and cancer. Correction of deficiency requires supplementation with higher levels of coenzyme Q than are available in the diet.

energy couplingantioxidanttransmembrane signalinggene expression
Previous SectionNext SectionKey teaching points:

• Coenzyme Q is needed for energy conversion.

• Coenzyme Q is an essentialantioxidant.

• Coenzyme Q regenerates other antioxidants.

• Coenzyme Q stimulates cell growth and inhibits cell death.

• Decreased biosynthesis may cause deficiency.

Previous SectionNext SectionINTRODUCTION
The point to emphasize is that coenzyme Q has several biochemical functions [1]. The well recognized functions are in mitochondrial energy coupling and its action as a primaryregenerating antioxidant. Less well established functions include oxidant action in the generation of signals and control of cellular redox state. By participation in transmembrane electron transport coenzyme Q can carry reducing equivalents to the inside of vesicles or to the outside of cells. There is also evidence for a role in proton gradient formation in endomembranes and at the plasma membrane. Inaddition, there is evidence that coenzyme Q can take part in control of membrane structure and phospholipid status [2,3].

Coenzyme Q is 2,3-dimethoxy,5-methyl, 6-polyisoprene parabenzoquinone. The coenzyme Q10 found in humans has a polyisoprene chain containing 10 isoprene units (5 carbons each) or a total of 50 carbons. The all trans polyisosoprene ensures an affinity for the interior ofcell membranes. The two methoxy groups contribute to the specificity in enzyme action as may the methyl group. The fully substituted quinone ring does not allow addition reactions with thiol groups in the cell such as glutathione, thioredoxin or thioctic acid. The functional group is the quinone ring. By reduction of the quinone to quinol a carrier of protons and electrons is produced [4].Coenzyme Q is distributed in all membranes throughout the cell [5]. In mitochondria there are well defined protein binding sites on the enzymes involved in coenzyme Q oxidation reduction [6]. Enzymes in other membranes can be expected to have specific coenzyme Q binding sites, but these have not been defined. In addition there is coenzyme Q floating in the phospholipid bilayer of the membranes. The...