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Applied and Environmental Microbiology, February 2006, p. 981-985, Vol. 72, No. 2
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.2.981-985.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Characterization of an Agrobacterium tumefaciens D-Psicose 3-Epimerase That Converts D-Fructose to D-Psicose

Hye-Jung Kim,{dagger}, Eun-Kyung Hyun,{dagger} Yeong-Su Kim,{dagger}, Yong-Joo Lee,{dagger} and Deok-Kun Oh*

Department of Bioscience and Biotechnology, Sejong University, Seoul 143-747, South Korea

Received 12 September 2005/ Accepted 5 November 2005

The noncharacterized gene previously proposed as the D-tagatose 3-epimerase gene from Agrobacterium tumefaciens was cloned and expressed in Escherichia coli. The expressed enzyme was purified by three-step chromatography with a final specific activity of 8.89 U/mg. The molecular mass of the purified protein was estimated to be 132 kDa of four identical subunits. Mn2+ significantly increased the epimerization rate from D-fructose to D-psicose. The enzyme exhibited maximal activity at 50°C and pH 8.0 with Mn2+. The turnover number (kcat) and catalytic efficiency (kcat/Km) of the enzyme for D-psicose were markedly higher than those for D-tagatose, suggesting that the enzyme is not D-tagatose 3-epimerase but D-psicose 3-epimerase. The equilibrium ratio between D-psicose and D-fructose was 32:68 at 30°C. D-Psicose was produced at 230 g/liter from 700-g/liter D-fructose at 50°C after 100 min, corresponding to a conversion yield of 32.9%.

* Corresponding author. Present address: Department of Molecular Biotechnology, Konkuk University, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, South Korea. Phone: 82-2-2049-6155. Fax: 82-2-3437-6106. E-mail: deokkun{at}konkuk.ac.kr.

{dagger} Present address: Department of Molecular Biotechnology, Konkuk University, Seoul 143-701, South Korea.

Applied and Environmental Microbiology, February 2006, p. 981-985, Vol. 72, No. 2
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.2.981-985.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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