D-Glucose isomerases

Hager M, Currie F, Holmberg K (2003) Organic Reactions in Microemulsions. 227 53-74 Hausler H, Stiitz AE (2001) d-Xylose (d-Glucose) Isomerase and Related Enzymes in Carbohydrate Synthesis. 215 77-114... 

The successful conversion of D-glucose into D-fructose on the industrial scale with immobilized D-glucose isomerase was a brilliant demonstration of the value of this kind of approach. Then followed a huge technical literature on enzyme immobilization, reviewed in Ref. 9 (page 353). We shall here restrict ourselves to the methods which have been utilized in the syntheses outlined in Tables II to X. We suggest to readers interested in theses techniques that they first use these methods. If they prove unsatisfactory, as there is a plethora of alternatives, other techniques, described in Refs. 8-10, may be tried a majority of readily available carbohydrate enzymes have been immobilized, often in several different ways. 

In many instances, the D-glucose isomerase occurs as an intracellular enzyme, although a number of organisms have been identified as producers of extracellular D-glucose isomerase. The following discussion will be concerned primarily with D-glucose isomerase prepared from Streptomyces sp. of the type described by Takasaki and Tanabe.37... 

D-Glucose isomerase from a Streptomyces species consists of four subunits, each39 of molecular weight —41,500. The specific activity of the pure enzyme is 20,000 IGIU per g. 

In general, D-glucose isomerases require a divalent cation such as Co2+, Mg +, or Mn2+ for their catalytic action.40 The D-glucose isomer-ases usually function well in the pH range of 6.5 to 8.5, and at temperatures from 40°C (104°F) to as high as 80°C (176°F), depending upon the source of the enzyme. 

The catalytic effect of D-glucose isomerase is inhibited by Cu2+, Hg2+, and Zn2+, and, to some extent, by Ca2+. Other inhibitors are xyli-tol and D-glucitol.41... 

The D-glucose isomerase derived from a Streptomyces sp. is relatively stable under the conditions of commercial use. These commercial conditions involve the use of the isomerase in fixed form, high concentrations of D-glucose in the substrate, and the presence of such divalent cations as Mg2-1-, and of hydrogensulfite ions. All of these conditions tend to protect the enzyme from inactivation. Generally, the... 

The kinetics of the D-glucose-D-fructose isomerization reaction catalyzed by soluble D-glucose isomerase at a specified concentration of substrate can be related to a simple concept of an enzyme-catalyzed, reversible reaction. 

The isomerizations conducted with D-glucose isomerase conform quite well to equation 5. 

D-Glucose isomerase becomes inactivated at a rate approximately first-order with respect to the concentration of isomerase. Equation 4 may be modified to... 

The rate of the isomerization reaction, catalyzed by a given quantity of D-glucose isomerase in the fixed form, suspended in a given volume of D-glucose solution in cases studied, is about the same as when the same quantity of D-glucose isomerase in the soluble form is dissolved in that volume of the solution of D-glucose. 

In general, the fixed D-glucose isomerase systems have many advantages with respect to enzyme use, efficiency, ease of handling, and adaptability to continuous-reactor operation. Methods have been described that employ a continuously stirred tank-reactor provided with a semipermeable membrane through which the isomerized liquor, having the steady-state composition, is removed from the reaction medium at the same rate as fresh substrate is introduced into the reactor.47 The soluble enzyme is retained in the reaction zone, because it is held back by the semipermeable membrane, and fresh enzyme may be added as needed, to compensate for enzyme inactivation, to the reaction zone with the fresh substrate. 

D-Glucose isomerases are exceptionally stable enzymes and the industrial... 

H. Hausler, H. Weber, and A. E. Stiitz, D-Xylose (D-glucose) isomerase (EC 5.3.1.5) observations and comments concerning structural requirements of substrates as well as mechanistic features, J. Carbohydr. Chem., 20 (2001) 239-256. 

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