| Xanthine oxidase (XOD, EC 1.1.3.2) is a key enzyme in the catabolism of purines path way, which mainly catalyzes the conversion of hypoxanthine and xanthine to xanthine and uric acid, respectively. It is also a complex molybdoflavoenzyme that exists in as an available oxidoreductase in all kinds of organisms. Microorganism, which produced xanthine oxidase, mainly were bacterium, streptomycete and pseudomonas. Xanthine oxidase has been used as clinical agent for anti-tumor and reperfusion injury.A mutant M3 was obtained with high xanthine oxidase activity by treating Arthrobacter X7 with physical and chemical co-mutagenesis. Xanthine oxidase activity of M3 was 2.07 times as that of Arthrobacter X7. The incubation period of M3 was shortened by 4 hours. As an intracellular induced enzyme,xanthine oxidase could be induced by different compounds. Based upon the xanthine oxidase activity and the production cost, several samples of chemicals were tested to compare their inducing effects on Arthrobacter M3, and hypoxanthine was found to be the optimal inducer. The study of hypoxanthine induced condition, indicated the xanthine oxidase activity of mutant M3 would be the highest when 3 g/L hypoxanthine was added to the culture in the prophase of the fermentation. Compared with xanthine inducing effect, xanthine oxidase activity of Arthrobacter M3, induced with hypoxanthine, were increased by 70.6%.Using hypoxanthine as inducer, the medium components for xanthine oxidase production and culture condition were further optimized, in order to improve the xanthine oxidase activity of strain M3. The optimization of culture medium components and flask culture condition resulted the xanthine oxidase yield and dry cell weight of cells reached to 4598.7 U/L and 8.87 g/L respectively. The xanthine oxidase production of cell unit from Arthrobacter M3 was 13.1 times higher than that of Arthrobacter X7. Xanthine oxidase yield of strain M3 was 6.2 times higher than the highest-level from the domestic report.
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