Mutarotases

7 Mutarotases (For a treatment of enzymological terms and concepts see Chapter 5). Mutarotases ensure that the mutarotation of sugars in vivo is much faster than spontaneous, and thus couples various transport systems and metabolic pathways. The relatively non-specific aldose mutarotases isolated 

Detailed mechanistic studies have been carried out with the E. coli enzyme, which is more active than the L. lactis enzyme, with kcat/ m for galactose 

The use of NMR techniques, rather than polarimetry, to monitor muta-rotation, as with the spontaneous reaction, allowed accelerations of particular conversions of sugars to be directly monitored. Saturation difference measurements indicated that three proteins from Escherichia coli, RbsD, FucU sic) and YiiL, of previously unknown function, had mutarotase activity.RbsD interconverted the (3-pyranose and (3-furanose forms of ribose, without any 

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Sucrose (3-Fructosidase and mutarotase and glucose oxidase Biotechnology... 

Starch Enzymatic Amyloglucosidase, mutarotase, glucose oxidase and catalase co-immobilised on either nylon net or activated collagen membrane Vrbova et al. (1993)... 

A mutarotase is an enzyme that oata lyses the irtter-conversfon of alpha and beta forms of... 

This enzyme [EC 5.1.3.3], also known as mutarotase, catalyzes the epimerization of the hemiacetal carbon atom of aldoses (thus, anomerization). Hence, a-D-glu-cose is reversibly converted to /3-D-glucose. Other sugars can act as substrates (e.g., L-arabinose, D-xylose, D-galac-tose, maltose, and lactose). 

TRANSITION-STATE ANALOGUE MULTISUBSTRATE MECHANISMS MUSCLE MASS DETERMINATION BY ISOTOPIC TRACERS MUTAROTASES ANOMERS... 

The continuous configurations depicted in Figs 5.12.D1 and 5.12.D2 were designed by Nieman s group for application of this sensor to the determination of sucrose (and glucose) in soft drinks, breakfast cereal and cake mix [36]. The analyte is converted into /3-D-glucose, to which the sensor is responsive, in two reaction steps that are catalysed by invertase (INV) and mutarotase (MUT) ... 

The oxidation reactions of luminol and lucigenin can be used to assay for H Oj. For example, analysis of glucose in biological systems can be achieved using a three-enzyme system of mutarotase, glucose oxidase and horseradish peroxidase by correlation with the amount of HjOj released. Similarly, cholesterol can be measured using cholesterol oxidase. The fact that the rate of luminol oxidation depends on the concentration of the catalyst can be used as a method for determination of Co +, Fe +, Cr + and Mn + and other catalysts.Some examples of the use of luminol, isolumi-nol and their derivatives in immunoassays are shown in Table 3.11. ... 

Many reactions that are promoted by enzymes can also be catalyzed by acids or bases or by both. An example is mutarotation, the reversible interconversion of the a- and (i-anomeric forms of sugars (Eqs. 4-1 and 9-86). This reaction is catalyzed by a specific mutarotase and also by inorganic acids and bases. 

The majority of the many methods used to study the composition of equilibrium solutions of carbohydrates examine the mixture without separating the individual components. With the discovery that the anomeric forms of sugars could be readily separated by gas chromatography of their tri-methylsilyl ethers, a new approach to the problem was found. A protocol was developed for the direct gas chromatographic analysis of the amount of each anomer present in an aqueous solution. The protocol can be used on the micro scale and can be used in enzyme assays such as that for mutarotase. The method has been made more effective by combining gas chromatography with mass spectrometry. It is shown how mass spectral intensity ratios can be used to discriminate anomers one from another. The application of these methods to the study of complex mutarotations is discussed. 

Figure 5. Mutarotase assay by the GLC-TMSi method. The enzyme preparation was obtained from hog kidney, and the conditions are those described previously (26).

Tphis review outlines the current knowledge of the enzyme mutarotase " (aldose-l-epimerase) and evaluates the evidence that it may have evolved from an origin in primitive bacteria into an important transport system for sugars in higher organisms. 

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