Enzyme Activity


Hydrolysis of Maltodextrin by α-amylase

An important industrial enzyme α-amylase hydrolyses starch, glycogen, and related polysaccharides by randomly cleaving internal 1,4-glucosidic linkages. It is used, for example, as an additive in detergents, for removal of starch sizing from textiles and proper formation of dextrin in baking. The figure above illustrates the ultrasonic (HR-US 102) monitoring of enzyme activity of α-amylase at 25C through the measurements of changes in ultrasonic velocity during the course of a hydrolysis of 10.4 mg/ml solution (0.02 M phosphate buffer, pH 6.9) by the enzyme.

Five microlitres of a 2 mg/ml amylase solution was added to a 1ml ultrasonic cell filled with maltodextrin solution in 0.02 M phosphate buffer at ten minutes of run. The hydrolysis of the maltodextrin by amylase causes an increase in ultrasonic velocity, because the hydration level of the product is higher than that of the maltodextrin substrate. The ultrasonic velocity curve was recalculated into the time dependence of the amount of substrate hydrolysed, i.e. the kinetic profile of the reaction. The enzyme activity calculated from this curve is 90 units/mg amylase (1 unit is defined as the amount of enzyme activity which liberate 1.0 mg of maltose in 1 min at 25C).  Ultrasonic attenuation decreases during the reaction (insert in the Figure above shows data at 14 MHz) as a result of a decrease in molecular weight of the substrate.  This decrease in the length of the substrate reduces the high frequency viscosity of the solution and therefore the attenuation of ultrasound. This provides independent information on the change of molecular weight of the substrate in this reaction.

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