Enzyme Sequence Sensors for Disaccharides

In biosensors for the determination of sucrose, lactose, and maltose, invertase (EC 3.2.1.26), [3-galactosidase (EC 3.2.1.23), maltase (EC 3.2.1.20), or myrosinase (EC 3.2.3.1) are coupled sequentially with GOD. Since the hydrolysis of disaccharides does not lead to an equilibrium mixture of a- and (3-glucose, the inclusion of mutarotase (EC 5.1.3.3) has proved useful. Oligo- and polysaccharides can be assayed by coupling glucoamylase (EC 3.2.1.3) or cellulase (EC 3.2.1.4) with GOD. 

The determination of sucrose in the microbiological and food industry is of a similar importance as the determination of glucose in the clinical laboratory. Sucrose consists of (3-D-fructose and a-D-glucose linked to each other by the glycosidic OH-groups  

Various research groups have developed enzyme electrodes for the determination of sucrose. The operational parameters of these sensors are listed in Table 10. 

In invertase-GOD electrodes glucose is formed in the following sequence of reactions  

With an excess of invertase and GOD in the enzyme membrane the total rate of sucrose determination is limited by the spontaneous mutarotation. Therefore the sensitivity towards sucrose is only about 10% of that for glucose (Scheller and Karsten, 1983). Kinetic (dl/dt) measurement even gives only 1% of the glucose signal at the same sucrose concentration. Application of coimmobilized mutarotase gives rise to an increase of the sensitivity by a factor of 6 for stationary measurement 

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