Enzymes phosphoglucose isomerase

This reaction, which enables the sum of glucose + fructose to be determined, is catalysed by the enzyme phosphoglucose-isomerase (PGl) ... 

The glucose-6-phosphate formed in the first reaction is rearranged to produce the structural isomer fructose-6-phosphate. The enzyme phosphoglucose isomerase catalyzes this isomerization. The result is that the C-1 carbon of the six-carbon sugar is exposed it is no longer part of the ring structure. Examination of the open-chain structures reveals that this isomerization converts an aldose into a ketose. 

The end result of either of these reaction schemes is glucose-6-phosphate, which is now isomerized to fructose-6-phosphate by the enzyme phosphoglucose isomerase ... 

The isomerization of D-glucose to D-fructose by way of an enediol intermediate is an important step in glycolysis, a complex process (11 steps) by which an organism converts glucose to chemical energy. The substrate is not glucose itself but its 6-phosphate ester. The enzyme that catalyzes the isomerization is called phosphoglucose isomerase. 

For the assay of enzymes with products and reagents that have no absorption, fluorescence or luminescence in the ultraviolet or visible region, developments in analytical infrared spectroscopy can be used. In particular, mid-Fourier transform infrared (mFTIR) spectroscopy has been successfully applied to the determination of enzyme activities and kinetics, e.g. of /i-fructosidasc, phosphoglucose isomerase and polyphenol oxidase [90]. The method could very well be a tool that may also be applied to a variety of other enzyme classes. The potential of high-throughput applications, however, has yet to be demonstrated. 

C. J. Jeffery, B.J. Bahnson, W. Chien, D. Ringe, and GA. Petsko. 2000. Crystal structure of rabbit phosphoglucose isomerase, a glycolytic enzyme that moonlights as neuroleukin, autocrine motility factor, and differentiation mediator... 

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. 

Xylose isomerase has a wide substrate specificity, and 3-, 5-, or 6- substituted glucose and fructose are isomerized by this enzyme. Since this enzyme requires the 4-OH group for hexoses to be substrates, phosphoglucose isomerase instead of xylose isomerase is used for the synthesis of 4-substituted fructose as described below. 

Phosphoglucose isomerase catalyzes an equilibrium between glucose-6-phosphosphate and fructose-6-phosphate. This enzyme is usually in excess and produces an equilibrium mixture of the two hexophosphates. 

The enzyme name, phosphoglucose isomerase, provides clues to the reaction that is being catalyzed (Section 20.1). Isomerase tells us that the enzyme will catalyze the interconversion of one isomer into another. Phosphoglucose suggests that the substrate is a phosphorylated form of glucose. 

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