| Ubiquinone (UQ), also known as Coenzyme Q. is an essential redox component of the aerobic respiratory chains of bacteria and mitochondria. UQ-10 has recently attracted increasing attention with regard to its vital roles as an antioxidant, and apparently, in gene regulation. Over the last two decades, UQ-10 has been successfully used as an orally administered prophylaxis and in therapy for a great variety of diseases because of its inert toxicity or scarce side effects. Since early clinical trials with UQ-10 were focused on heart disease due to the known high UQ-10 content of the myocardium and to the high amount of energy required for normal heart function; several other widespread and age-related diseases attributed to either disturbed mitochondrial function or oxidative stress have been studied with UQ-10 supplementation. With the increasing demand for its application in various fields, attempts have been made for the biotechnological production of UQ-10．Decaprenyl diphosphate synthase (dps) catalyzes the consecutive condensation of isopentenyl diphosphate with allylic diphospahtes to produce decaprenyl diphosphate, which is used for the side chain of UQ-10．Owing to be an efficient producer of UQ-10, Agrobacterium tumcfaciens dps gene was cloned and incorporated in the expression strain of Escherichia coli. The level of ubiquinone-10 in the recombinant cells was greater than that of ubiquinone-8, which is intrinsic in E. coli cells. Furthermore, the production of UQ-10 was higher than UQ-8．To establish an efficient expression system for UQ-10 production, we used genes, including ubiC, ubiA and ubiG involved in UQ biosynthesis in E. coli, to construct a better co-expression system. The expression coupled by dps and ubiCA was effective for increasing UQ-10 production by five times than that by expressing single dps gene in the shake flask culture. Based on the information derived from shake flask cultures, a high cell density fermentation process was performed for large scale UQ-10 production. Throughout the fermentation, dissolved oxygen concentration was kept at 20% above air saturation via closed-loop controls operating the two output variables of stirrcr speed and increasing the aeration. This fed-batch method prevented any significant accumulation of acetate and other metabolic by-products. With application of oxygen enriched aeration and an appropriate medium design, a cell concentration of 85．40 g L and 94．58 g L dry cell weight (DCW), and UQ-10 content of 50．29 mg L and 45．86 mg L was obtained after 32．5 h and 27．5 h cultivation subsequent to IPTG and lactose induction, respectively. In addition, plasmid stability was maintained at high level throughout the fermentation...
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