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Production of ubiquinone as a side product

Ubiquinone (coenzyme Q) is an intermediary in redox reactions. Ubiquitous in living forms, widespread in the cells, ubiquinone is an essential component of the mitochondrial respiratory chain, where it acts as a carrier of hydrogen atoms. Ubiquinone contains a quinone ring and a terpenoid chain, which are synthesised separately. The hydrophobic terpenoid tail serves to anchor the coenzyme to membranes.

Industry appreciates the beneficial effects of ubiquinone on health. It has antioxidant properties and protects against highly reactive chemicals and free radicals. It reduces blood pressure and prevents congestive heart failure. The amounts in the body varies in different organs, with highest concentrations in the heart, and normally declines with age.

The Zygomycetes Blakeslea trispora and Phycomyces blakesleeanus accumulate ubiquinone, ß carotene, various different sterols, and other terpenoids, all of them produced via the mevalonate pathway. These fungi are used or could be used for the industrial production of these terpenoids, edible oil, chitosan, and various organic acids.

By measuring the specific radioactivity of terpenoids made from radioactive mevalonate, leucine or acetate in the presence of excess glucose in wild types and mutant strains we have concluded that these fungi have separate subcellular compartments for the production of carotene, sterols and triacylglycerols. The terpenoid moiety of ubiquinone is synthesised in the same compartment as ergosterol. These compartments contain separate pools of all their common metabolites, beginning from acetyl-CoA. Mevalonate carbon atoms do not find their way back to general metabolism, i. e., these fungi lack the shunt pathway.

The compartments are regulated independently. The very large variations in carotene content caused by many environmental and genetic changes are not accompanied by variations in the ubiquinone content, which is about 0,3 mg ubiquinone / g dry mass in both fungi. The ubiquinone content increases when the cultures grow on leucine or acetate as carbon sources and is not affected by illumination. The variations are modest: Blakeslea contains up to 0,8 and Phycomyces up to 0,6 mg ubiquinone/ g dry mass depending in the media composition. Phycomyces, but not Blakeslea, increases the production of ubiquinone in presence of oligomycin.

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University of Sevilla
Departamento de Genetica, Apartado 1095
E-41080 Sevilla
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