Glucose-to-fructose

S (2)-hydroxy-3-butenenitrile from acrolein and HCN trans hydrocyanation using, for instance, acetone cyanohydrin Hydrolysis of nitriles to amides, e.g. acrylonitrile to acrylamide Isomerization of glucose to fructose Esterifications and transesterifications Interesterify positions 1 and 3 of natural glycerides Oxidation of glucose to gluconic acid, glycolic acid to glyoxalic acid... 

Unlike reactions involving microorganisms, in enzyme reactions the catalytic agent (the enzyme) does not reproduce itself. An example in the use of enzymes is the isomerization of glucose to fructose ... 

A similar interpretation is possible for the Lobry de Bruyn rearrangement of glucose to fructose ... 

Xylose isomerases (EC 5.3.1.5), often referred to as glucose isomerase, have been studied extensively, in large part because of their use in the conversion of glucose to fructose for high-fructose corn syrup (HFCS). The world market for HFCS is expected to reach a total of 7.9 million metric tons in 1990 which, at a cost of 0.20/LB, would amount to 3.2 billion (i), and sales of xylose isomerase is expected to be about 15 million (T. Wallace, International Biosynthetics, personal communication). Research on xylose isomerase has produced DNA sequences of the gene from a number of bacterial strains, including the detailed structure of the xylose operon (2-7). In addition, x-ray crystallographic studies (8), kinetic measurements (9), and the use of inhibitors (10,11) have led to descriptions of the location of the active site and mechanistic models of its activity. 

Initial Discoveries. Xylose isomerase activity was initially found in 1953 in extracts of Lactobacillus pentosus (14), followed by similar activities in extracts of Pseudomonas hydrophila and Pasteurella pestis in the mid-1950s (15-17). An enzyme activity that was found to convert glucose to fructose was discovered in 1957 (18). This activity, found in sonicated extracts from Pseudomonas hydrophila, was enhanced in the presence of... 

Production of HMF from glucose was also evaluated using titanium and zirconium oxides as solid acid catalysts in hot compressed water (473 K) [78-80], Interestingly, it was found that the Zr02 catalyst acts as an acido-basic catalyst. Therefore, Zr02 was able to promote a tandem reaction involving (1) the isomerization of glucose to fructose and (2) the dehydratation to fructose to HMF (yield of HMF = 20% Scheme 8). 

Problem 22.12 Osazones are converted by PhCHO to 1,2-dicarbonyl compounds called osones. Use this reaction to change glucose to fructose. 

In the preparatory phase of glycolysis, ATP is invested to convert glucose to fructose 1,6-bisphosphate. The bond between C-3 and C-4 is then broken to yield two molecules of triose phosphate. 

Kiewer (20) indicated that for the vinifera grapes studied, glucose breakdown apparently occurred when grapes were in an overripe condition which resulted in a sharp decrease in the glucose/fructose ratio. Normal ratio during the ripe period was considered to be ca. 1.00 0.10. This was in accord with the observation with Concord (25) that sucrose was synthesized in the leaves and translocated to other vine parts where hydrolysis resulted in 1 1 ratio of glucose to fructose. 

Glucose oxidase, which converts glucose to dextrose and levulose. Isomerase, which converts glucose to fructose. 

The basic patent coverage for use of xylose isomerase to convert glucose to fructose was lost in 1975 as the result of a civil action suit between CPC International and Standard Brands. Tins enabled development of alternate processes. By 1978. the estimated US production volume was 3.5 x 109 lb and consisted mostly ot syrups containing 42% D-fructose sold at a 71 % solids level (Antrim et al.). The introduction of large scale liquid chromatographic purification of the fructose enabled production of a 55% fructose which could be used in soft drinks in place of invert from sucrose. 

Glucose Isomerase This enzyme is found in many organisms and. in practice, is used in the form of entrapped cells or bound to ion-exchange resins. Glucose isomerase converts glucose to fructose, one of the principal components of table sugar. 

Glucose Isomerization. Enzymatic isomerization of glucose to fructose provides a real alternative to sugar (sucrose) derived from sugarcane or sugarbeets. The commercial product obtained is known as high fructose com syrup (HFCS). Two grades of the syrup have become established on the world market, HFCS-42 and HFCS-55, which contain 42 and 55% fructose on dry substance basis. These products account for over one-third of the caloric sweetener market in the United States. 

The isomerization of glucose to fructose, catalyzed by the enzyme xylose isomerase, is by far the largest-scale biocatalytic process. Already known for several decades,... 

The conversion step to high-fructose syrup takes place in a reactor containing immobilized glucose isomerase. Although nonenzymic processes to isomerize glucose to fructose have been developed,11 these processes result in undesirable by-products of ash, color, and flavor, and other faults. 

Considerable effort based on research work initiated in the 1950s resulted in enzyme technology able to convert glucose to fructose on a commercial scale.32 34 Current production of high-fructose syrups generally uses immobilized, rather than soluble, enzymes. Sources of the enzyme include Streptomyces, Bacillus, Actinoplanes and Arthrobacter species. 

The isomerization of glucose to fructose has been extensively studied and the mechanism is well-documented.35-37 The reaction is essentially first order and reversible, following Michalis-Menten characteristics shown in Figure 21.9. 

Fructans are found within the vacuole, and catabolic and anabolic enzymes and alterations occur therein (Carpita et al., 1991 Wiemken et al., 1986). Alterations in the fructans require the input of energy, most of which is thought to be associated with the recycling of glucose to fructose in the cytoplasm. It has been estimated that the cost is between 4 and 8% of the total mass of assimilates (Edelman, 1963 Meijer and Mathijssen, 1991). 

One of the enzymes that has been used on a large scale is glucose/xylose isomerase, which catalyzes the rearrangement of glucose to fructose, to yield a product with a sweet taste like sucrose. The enzyme is present in Streptomyces spp. as well as a few other organisms. Once again, the native host strain has been improved for production of glucose isomerase. 

Glucose Isomerase. The biggest success story in the enzyme industry has to be glucose isomerase. The very first report of an enzyme that converts glucose to fructose was in 1957 (10). In less than 20 years the enzyme was studied, tailored into a cost effective immobilized form and put into production to make a commodity corn syrup product. In less than 30 years from its first description, it became the largest commercially used immobilized enzyme and responsible for making one of the world s major sweeteners. Since... 

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