Xylose-glucose isomerase

The xylose-glucose isomerase was purified to homogeneity from C. thermosulfurogenes (Lee, C.-Y and Zeikus, J. G., Biochem. J., in pressV, and, its general... 

Table V. Biochemical Characteristics of C. thermosulfurogenes Strain 4B Xylose/Glucose Isomerase...

Interest in the bacterial ens me xylose/glucose isomerase has been driven by its use in the isomerization of ucose to fructose to produce high>fructose corn syrups, and in the isomerization of xylose to xylulose for the conversion of the more fermentable xylulose to ethanol In this work, a brief historical perspective is presented, followed by a summary of the current understanding of the enzyme s major features. Also, a useful compilation of available xylose isomerase DNA sequences is presented with annotation of some of the major areas identified as being of functional significance. The extent of homology between the xylose isomerases is discussed with reference to differences in their function. 

Transketolase catalyzes the reversible transfer of a hydroxyacetyl fragment from a ketose to an aldehyde. Because the ketose products formed by transketolase reactions are not acceptors for a consecutive transformation by the same enzyme, we have investigated the option to include a xylose (glucose) isomerase (Xyll E.C. 5.3.1.5), which has similar stereochemical specificity, for ketose to aldose equilibration (Scheme 2.2.5.13). Starting from racemic lactaldehyde 32a, the transketolase forms 5-deoxy-D-xylulose 35a, which indeed was accepted by the Xyll in situ for diastereospecific conversion into 5-deoxy-D-xylose 36a. The latter again proved to be a substrate of transketolase which completed a tandem operation to furnish 7-deoxy-sedoheptulose 37a as the sole bisadduct in 24% overall yield and in enantio- and diastereomerically pure quality [35, 36]. All four stereocenters of the resulting product are completely controlled by the enzymes during this one-pot operation. The procedure profits from the limited tolerance of the isomerase... 

Basic patent coverage for xylose (glucose) isomerase lost in lawsuit opened up development of new HFCS processes. 

S. -Y. Liu, J. Wiegel, and F. C. Gherardini, Purification and cloning of a thermostable xylose (glucose) isomerase with an acidic pH optimum from Thermoanaerobacterium strain JW/SL-YS 489, J. Bacteriol. 1996, 178, 5938-5945. 

B major axis near /J-strand 1 M R, M LE are missing final a-helix domains cover the C-terminal end of the barrel domain blocks N-terminus of the barrel mandelate racemase, muconate cycloisomerase, xylose (glucose) isomerase... 

Figure 6.8 Binding of a transition state analogue to (bottom), and proposed reaction mechanism of (top), xylose-glucose isomerases. 02 of the substrate (01 of the transition state analogue) must be deprotonated in order to bind both Mg " ions.

We describe here the enzymological characteristics and application of isomerases, especially D-xylose (glucose) isomerase, phosphoglucose isomerase, triose phosphate isomerase, L-rhamnose isomerase, L-fucose isomerase, maleate cis-trans isomerase, and unsaturated fatty acid cis-trans isomerase. N-Acetyl-D-glucosamine 2-epimerase is not an isomerase, but for convenience we will also describe the characteristics and use of the enzyme because this section deals with sugar-metabolizing enzymes. 

Isomerization of sugars sugar phosphates xylose (glucose) isomerase triosephosphate isomerase... 

Walfridsson, M., Bao, X., Anderlund, M., Lilius, G., Buelow, L., Hahn-Gaegerdal, B. (1996). Ethanolic fermentation of xylose with Saccharomyces cerevisiae harboring the Thermus thermophilus xylA gene, which expresses an active xylose (glucose) isomerase. Applied and Environmental Microbiology, 62(12), 4648 651,... 

The CO-factor imbalance generated by the first two steps in xylose metabolism could be entirely circumvented if the conversion of xylose to xylulose were to be catalyzed by the prokaryotic enzyme xylose isomerase (XI, Fig. 1). o-Xylose (glucose) isomerase EC 5.3.1.5 catalyses the reversible isomerization of o-xylose and D-glucose to D-xylulose and D-fructose, respectively. XI does not require redox cofactors and cannot generate cofactor imbalance during anaerobic xylose utilization. 

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