Observations of reaction intermediates and the mechanism of aldose-ketose interconversion by D-xylose isomerase.

Collyer, Charles A.; Blow, D. M.

doi:10.1073/pnas.87.4.1362

Cited by 88 publications

(71 citation statements)

References 21 publications

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“…Studies using deuterated solvents have shown that enzymes and bases perform the aldose/ketose transformation through a mechanism involving a cis 1,2-enediol intermediate, whereby the bonding electron pair at C-2 moves through the carbon skeleton to C-1 (Scheme 2A) (17,18). Kinetic studies of isomerization reactions report that certain acids and metals are able to transfer the hydrogen directly through a hydride shift between C-2 and C-1 (Scheme 2B) (19). Corma et al showed that Sn incorporated in the framework of zeolite Beta is a good catalyst for the MPV reaction between alcohols and ketones that requires adequate Lewis acidity in the catalyst to polarize the carbonyl group in the ketone while also coordinating both the alcohol and the ketone to facilitate a hydride shift between them (12,13).…”

Section: Resultsmentioning

confidence: 99%

Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

Moliner

Román‐Leshkov

Davis

2010

Proc. Natl. Acad. Sci. U.S.A.

884

831

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The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup (HFCS; reaction performed by enzyme catalysts) and recently is being considered as an intermediate step in the possible route of biomass to fuels and chemicals. Here, it is shown that a large-pore zeolite that contains tin (Sn-Beta) is able to isomerize glucose to fructose in aqueous media with high activity and selectivity. Specifically, a 10% (wt∕wt) glucose solution containing a catalytic amount of Sn-Beta (1∶50 Sn: glucose molar ratio) gives product yields of approximately 46% (wt∕wt) glucose, 31% (wt∕wt) fructose, and 9% (wt∕wt) mannose after 30 min and 12 min of reaction at 383 K and 413 K, respectively. This reactivity is achieved also when a 45 wt% glucose solution is used. The properties of the large-pore zeolite greatly influence the reaction behavior because the reaction does not proceed with a medium-pore zeolite, and the isomerization activity is considerably lower when the metal centers are incorporated in ordered mesoporous silica (MCM-41). The Sn-Beta catalyst can be used for multiple cycles, and the reaction stops when the solid is removed, clearly indicating that the catalysis is occurring heterogeneously. Most importantly, the Sn-Beta catalyst is able to perform the isomerization reaction in highly acidic, aqueous environments with equivalent activity and product distribution as in media without added acid. This enables Sn-Beta to couple isomerizations with other acid-catalyzed reactions, including hydrolysis/isomerization or isomerization/dehydration reaction sequences [starch to fructose and glucose to 5-hydroxymethylfurfural (HMF) demonstrated here].glucose isomerization | heterogeneous catalysis T he isomerization of sugars is a key reaction used in various relevant industrial processes. For instance, the conversion of glucose into fructose for the production of high-fructose corn syrups (HFCS) has become the largest immobilized biocatalytic process worldwide. HFCS have reached a global production exceeding 8 × 10 6 tons∕year (in the United States alone, per capita consumption of HFCS reached 37.8 lbs∕year in 2008) (1-3). In addition, the recent drive to use biomass as an alternative to petroleum for the production of fuels and chemical intermediates has triggered a renewed interest in carbohydrate chemistry. In this respect, glucose isomerization is a crucial step in the efficient production of valuable chemical intermediates, such as 5-hydroxymethylfurfural (HMF) and levulinic acid, from biomass; however, a heterogeneous isomerization catalyst (biological or inorganic) that can easily integrate glucose isomerization with the transformation of fructose into these intermediates is lacking (4, 5). Here, we present highly active heterogeneous inorganic catalysts for the isomerization of glucose that resemble the performance of enzymatic catalysts by generating remarkably high-fructose yields at glucose conversions near the reaction equilibrium. Furthermore, unlike enzymatic cat...

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Section: Resultsmentioning

confidence: 99%

Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

Moliner

Román‐Leshkov

Davis

2010

Proc. Natl. Acad. Sci. U.S.A.

884

831

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“…8 -barrel fold they have different catalytic mechanisms. d-Xylose isomerase exploits the hydride shift mechanism Collyer & Blow, 1990!. TIM follows the enolization mechanism Rose, 1975!, which has also been accepted for several other isomerases including both metal-dependent~mannose-6P, l-arabinose, and l-fucose isomerases!…”

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confidence: 99%

The mechanism of sugar phosphate isomerization by glucosamine 6‐phosphate synthase

et al. 1999

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Glucosamine 6-phosphate synthase converts fructose-6P into glucosamine-6P or glucose-6P depending on the presence or absence of glutamine. The isomerase activity is associated with a 40-kDa C-terminal domain, which has already been characterized crystallographically. Now the three-dimensional structures of the complexes with the reaction product glucose-6P and with the transition state analog 2-amino-2-deoxyglucitol-6P have been determined. Glucose-6P binds in a cyclic form whereas 2-amino-2-deoxyglucitol-6P is in an extended conformation. The information on ligand-protein interactions observed in the crystal structures together with the isotope exchange and site-directed mutagenesis data allow us to propose a mechanism of the isomerase activity of glucosamine-6P synthase. The sugar phosphate isomerization involves a ring opening step catalyzed by His504 and an enolization step with Glu488 catalyzing the hydrogen transfer from C1 to C2 of the substrate. The enediol intermediate is stabilized by a helix dipole and the E-amino group of Lys603. Lys485 may play a role in deprotonating the hydroxyl O1 of the intermediate.

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“…2). However, the amino acids involved in substrate binding and isomerization (5,8,9) and the spacing between them are well conserved. These residues are not situated in one domain, but they are spread out along the primary structure.…”

Section: This Fragment Was Sequenced In Both Directions Showingmentioning

confidence: 99%

“…The net traffic (calculated from [2], S. violaceoniger [3], A. missouriensis [4], Ampullariella species [5], Clostridium thermosulfurogenes [6], Clostridium thermohydrosulfuricum [7], B. subtilis [8], and E. coli [9]. Numbers are for the T. thermophilus enzyme.…”

Section: This Fragment Was Sequenced In Both Directions Showingmentioning

confidence: 99%

“…Genes from Escherichia coli (29), Bacillus subtilis (35), Clostridium species (10,17), Streptomyces species (11,15), Ampullariella species (27), and Actinoplanes missouriensis (2) have been sequenced. The crystal structure of Actinomycetes xylose isomerase, an (a/p)8 barrel, has been resolved (5,8,26), and the reaction mechanism has been gradually unraveled (9,17).…”

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confidence: 99%

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Xylose (glucose) isomerase gene from the thermophile Thermus thermophilus: cloning, sequencing, and comparison with other thermostable xylose isomerases

et al. 1991

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The xylose isomerase gene from the thermophile Thermus thermophilus was cloned by using a fragment of the Streptomyces griseofuscus gene as a probe. The complete nucleotide sequence of the gene was determined. T. thermophilus is the most thermophilic organism from which a xylose isomerase gene has been cloned and characterized. The gene codes for a polypeptide of 387 amino acids with a molecular weight of 44,000. The Thermus xylose isomerase is considerably more thermostable than other described xylose isomerases. Production of the enzyme in Escherichia coli, by using the tac promoter, increases the xylose isomerase yield 45-fold compared with production in T. thermophilus. Moreover, the enzyme from E. coli can be purified 20-fold by simply heating the cell extract at 85 degrees C for 10 min. The characteristics of the enzyme made in E. coli are the same as those of enzyme made in T. thermophilus. Comparison of the Thermus xylose isomerase amino acid sequence with xylose isomerase sequences from other organisms showed that amino acids involved in substrate binding and isomerization are well conserved. Analysis of amino acid substitutions that distinguish the Thermus xylose isomerase from other thermostable xylose isomerases suggests that the further increase in thermostability in T. thermophilus is due to substitution of amino acids which react during irreversible inactivation and results also from increased hydrophobicity.

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Observations of reaction intermediates and the mechanism of aldose-ketose interconversion by D-xylose isomerase.

Abstract: Crystallographic studies of D-xylose isomerase (D-xylose ketol-isomerase, EC 5.3.

Cited by 88 publications

References 21 publications

Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

The mechanism of sugar phosphate isomerization by glucosamine 6‐phosphate synthase

Xylose (glucose) isomerase gene from the thermophile Thermus thermophilus: cloning, sequencing, and comparison with other thermostable xylose isomerases

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