Characterization of a tetrameric inositol monophosphatase from the hyperthermophilic bacterium Thermotoga maritima.
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 V(max) (442 micromol min(-1) mg(-1)) that was much higher than the V(max) 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 Mg(2+) 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.
Chen
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L
Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02167, USA.
Roberts
M F
MF
D004795:Enzyme Stability; D006358:Hot Temperature; D006801:Humans; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008970:Molecular Weight; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification; D013379:Substrate Specificity; D020124:Thermotoga maritima / Q000201:enzymology*
D011994:Recombinant Proteins; D008094:Lithium; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase