Effects of pH on fungal amylase activity
November 25, 2011
In recent years, the uses of microorganisms have become a huge importance to industry and sparked a large interest into the exploration of enzyme activity in microorganisms. Amylase is one of the most widely used enzyme required for the preparation of fermented foods. Apart from food and starch industries, in which demand for them is increasing continuously, amylase is also used in various other industries such as paper and pulp, textiles, and medical labs. The global market for enzymes was about $2 billion in 2004 (Sivaramakrishnan et al., 2006).
Fungi belonging to the genus Aspergillus are most commonly used for the production of amylase. Traditionally, most of the production of amylase is carried out by submerged fermentation, a process which is a method for growing pure cultures of aerobic bacteria, and are incubated in a liquid medium subjected to continuous vigorous agitation. Because of the ease of handling and a greater control of the environmental factors like temperature and pH, microorganisms like Aspergillus can also be grown on moist solid materials in the absence of free-flowing water. This is called solid-state fermentation. Normally, the substrates fermented by solid-state include a variety of agricultural products such as rice, wheat, and soybeans. However, non-traditional substrates include an abundant supply of agricultural, forest and food-processing wastes (Young et al., 1995). A number of such substrates have been employed for the cultivation of microorganisms to produce host of enzymes and in this case, amylase.
Amylases are starch-degrading enzymes that catalyze the hydrolysis of internal glycosidic bonds in polysaccharides (Sivaramakrishnan et al., 2006). To be effective, enzymes require specific environmental and chemical conditions. For example, the slightest variation in pH levels can significantly influence the three-dimensional shape of the enzyme and its ability to be a functional enzyme. This means that if the enzyme is altered because of the slightest pH difference the substrate may not be able to bind to the enzyme’s active site. Therefore, rendering it inactive and unable to catalylse any form of a reaction.
For example, as pH increases there are fewer hydrogen ions in a solution making it less acidic and more alkaline like, which can lead to reactions taking place that can alter the protein molecule’s functional group (amino acids) this causes enzymes to change their shape. Similarly, as pH decreases there are more hydrogen ions in a solution making it more acidic. This too leads to the alteration of a protein molecule’s functional group, and causes enzymes to change their shape. Consequently, with the exception to human digestive enzyme, most enzymes have an optimal range. At the slightest pH change, the active site of the enzyme is altered, which prohibits a specific substrate from binding to the active site and will no longer fit. pH that is sufficiently changed will completely alter an enzyme. Unlike extreme heat that causes an enzyme irreparably damage or become denatured, pH changes are reversible. Restore the pH to its original level, and the enzyme will return to its original capability (Richardson et al., 2002).
The structure of an enzyme has its active site on the surface and is complementary to the substrate. Here, the substrate and the enzyme create a chemical reaction to form a product. Most enzyme structures are a tertiary structure that is formed by weak R-group interactions that gives the enzyme its unique form, and held together by hydrogen bonds, ionic bonds, Vann der Waals interactions, and disulfide bridges to reinforce the protein structure (Weslake et al., 1983). Any change or disruption to these interactions and the enzyme will denature. Therefore, an enzyme’s shape depends upon its ability to perform at its...
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