Starch hydrolases

H. M. Jespersen, E. A. MacGregor, M. R. Sieiks, and B. Svensson, Comparison of the domain-level organization of starch hydrolases and related enzymes, Biochem. J., 280 (1991) 51-55. 

Table I. Complete Sequence of Starch-Hydrolases and Related Ernies...

Figure 4. Alignment of short segments from starch-hydrolases and related enzymes as guided by GlulSO in glucoamylase, Asp505 of isomaltase (24), and the putative catalytic Aspl97 of porcine pancreatic a-amylase (15) and substrate binding Asp206 of Taka-amylase A (14). The sequences for the remaining enzymes are taken from the Refs, in Table I.

Figure 8. Schematic domain level organization of starch-hydrolases and related enzymes (see text for further details).

Glycoside hydrolases (glycosidases) are essential and consequently widely abundant enzymes in all living systems that rely on the processing of carbohydrates. From the degradation of such polysaccharides as starch, cellulose, or chitin to the highly... 

A great advantage of spectrophotometric assays is that they can be carried out in microtiter plates or as filter paper assays, thus allowing a high sample throughput coupled with small sample volumes. Such systems were used for example for the screening of epoxide hydrolases [34]. A classical example of activity tests is for amylolytic enzymes where starch agar plates are stained with iodine after a certain reaction time. The radius of clear spots is a measure of the reaction rate [35]. 

The pretreatment of wastewater with hydrolases or acids is one of the best ways to overcome this obstacle, because in this way the big polymer molecules can be decomposed to smaller units, which can be measured by the biosensor. The positive effect of an enzymatic pretreatment of wastewater prior to sensorBOD measurement was demonstrated [53, 66]. In these investigations, different types of wastewaters, which contained milk powder, starch, or cellulose, were treated by proteases, a-amylases, and cellulases or a mix of these enzymes, respectively. This pretreatment resulted in a good correlation between sensorBOD and the conventional five-day BOD, while the sensorBOD values for untreated wastewater were significantly lower (see Table 6). As an example, the sensorBOD of a wastewater from a paper factory increased approximately to the fourfold value when treated by a mixture of cellulase and -glucosidase. 

The role of the enzymes is three-fold. Firstly there is the use of very thermostable df-amylases to pre-thin the gelatinised starch, reducing its viscosity so that it can be easily handled and further processed. This process is conceptually very similar to many other commercial uses of hydrolases, especially proteases and glycosidases. Pre-thinning takes place at 105°C and the thermostable df-amylase from B. licheniformis actually has a temperature optimum of almost 100°C. 

A number of starch-converting enzymes belong to a single family termed the a-amylase family or family 13 hydrolases. This group of enzymes shares common characteristics such as an eight-stranded a/p barrel structure, the ability to hydrolyze 1,4-a-D-glucosidic linkages of attached polysaccharides in a-conformation, and conserved amino acid residues in the active sites of the enzymes (van der Maarel et al. 2002). 

Currently, only hydrolases (amylases) are used to modify starch. The use of amylases to produce products derived from hydrolysis of starch is described in Chapters 7,20, 21 and 22. Starch hydrolyzates with good adhesion property that can be applied at high solids to minimize the energy required to remove moisture after application are very desirable for coating food items with seasonings, flavors and colorants. This property can be achieved by treating starch with an amylase or amylases to a dextrose equivalency (DE) (see Chapter 21) of 2-40.228 Waxy maize is the preferred starch. 

The general mode of action of detergent enzymes is quite similar. Detergent enzymes usually belong to the class of so-called hydrolases. These enzymes are able to split polymeric structures of stubborn soils such as proteins (e.g. blood, egg or starch) by hydrolysis and the fragments of the polymeric structures have to be subsequently detached by the surfactant system. 

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