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Appl Environ Microbiol, July 1998, p. 2357-2360, Vol. 64, No. 7
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Thermotoga neapolitana Homotetrameric Xylose Isomerase Is Expressed as a Catalytically Active and Thermostable Dimer in Escherichia coli

J. Michael Hess,1,dagger Vladimir Tchernajenko,2 Claire Vieille,2 J. Gregory Zeikus,2,3 and Robert M. Kelly1,*

Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-79051; Department of Biochemistry, Michigan State University, East Lansing, Michigan 488242; and Michigan Biotechnology Institute, Lansing, Michigan 489093

Received 9 February 1998/Accepted 9 April 1998

The xylA gene from Thermotoga neapolitana 5068 was expressed in Escherichia coli. Gel filtration chromatography showed that the recombinant enzyme was both a homodimer and a homotetramer, with the dimer being the more abundant form. The purified native enzyme, however, has been shown to be exclusively tetrameric. The two enzyme forms had comparable stabilities when they were thermoinactivated at 95°C. Differential scanning calorimetry revealed thermal transitions at 99 and 109.5°C for both forms, with an additional shoulder at 91°C for the tetramer. These results suggest that the association of the subunits into the tetrameric form may have little impact on the stability and biocatalytic properties of the enzyme.

* Corresponding author. Mailing address: Department of Chemical Engineering, North Carolina State University, Raleigh, NC 27695-7905. Phone: (919) 515-6396. Fax: (919) 515-3465. E-mail: kelly{at}che.ncsu.edu.

dagger Present address: Novo Nordisk Biochem North America, Franklinton, N.C. 27587.

Appl Environ Microbiol, July 1998, p. 2357-2360, Vol. 64, No. 7
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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