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Applied and Environmental Microbiology, October 1999, p. 4559-4567, Vol. 65, No. 10
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Characterization of a Tetrameric Inositol Monophosphatase from the Hyperthermophilic Bacterium Thermotoga maritima

Liangjing Chen and Mary F. Roberts*

Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02167

Received 21 May 1999/Accepted 15 July 1999

Inositol monophosphatase (I-1-Pase) catalyzes the dephosphorylation step in the de novo biosynthetic pathway of inositol and is crucial for all inositol-dependent processes. An extremely heat-stable tetrameric form of I-1-Pase from the hyperthermophilic bacterium Thermotoga maritima was overexpressed in Escherichia coli. In addition to its different quaternary structure (all other known I-1-Pases are dimers), this enzyme displayed a 20-fold higher rate of hydrolysis of D-inositol 1-phosphate than of the L isomer. The homogeneous recombinant T. maritima I-1-Pase (containing 256 amino acids with a subunit molecular mass of 28 kDa) possessed an unusually high Vmax (442 µmol min-1 mg-1) that was much higher than the Vmax of the same enzyme from another hyperthermophile, Methanococcus jannaschii. Although T. maritima is a eubacterium, its I-1-Pase is more similar to archaeal I-1-Pases than to the other known bacterial or mammalian I-1-Pases with respect to substrate specificity, Li+ inhibition, inhibition by high Mg2+ concentrations, metal ion activation, heat stability, and activation energy. Possible reasons for the observed kinetic differences are discussed based on an active site sequence alignment of the human and T. maritima I-1-Pases.

* Corresponding author. Mailing address: Merkert Chemistry Center, Boston College, Chesnut Hill, MA 02167. Phone: (617) 552-3617. Fax: (617) 552-2705. E-mail: mary.roberts{at}bc.edu.

Applied and Environmental Microbiology, October 1999, p. 4559-4567, Vol. 65, No. 10
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.