Amylases (Types, Sources, Mode of Action & Applications)

Amylases (Types, Sources, Mode of Action & Applications)

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  Amylases (Types, Sources,Mode of Action & Applications) Amylases are important hydrolase enzymes which have been widely used since many decades. These enzymes randomly cleave internal glycosidic linkages in starch molecules to hydrolyze them and yield dextrins and oligosaccharides. Among amylases α-Amylase is in maximum demand due to its wide range of applications in the industrial front. α-Amylase can be produced by plant or microbial sources. The ubiquitous nature, ease of production and broad spectrum of applications make α-Amylase an industrially important enzyme. Types of Amylase 1. α-Amylase α-Amylase (E.C.3.2.1.1) is a hydrolase enzyme that catalyses the hydrolysis of internal α-1, 4- glycosidic linkages in starch to yield products like glucose and maltose. It is a calcium metalloenzyme i.e. it depends on the presence of a metal co factor for its activity. The a-amylase family is the largest family of glycoside hydrolases, transferases, and isomerases, comprising 30 different enzyme specificities. These enzymes are classified into four groups: endoamylases, exoamylases, debranching enzymes, and transferases. Endo- hydrolases act on the interior of the substrate molecule, whereas exo-hydrolases act on the terminal non reducing ends. α-Amylase has become an enzyme of crucial importance due to its starch hydrolysis activity and the activities that can be carried out owing to the hydrolysis. They are biodegradable and work at milder conditions than chemical catalysts and hence preferred to the latter. 2. β – Amylase β-Amylase (EC 3.2.1.2) is an exo-hydrolase enzyme that acts from the nonreducing end of a polysaccharide chain by hydrolysis of α-1, 4-glucan linkages to yield successive maltose units. Since it is unable to cleave branched linkages in branched polysaccharides such as glycogen or
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  amylopectin, the hydrolysisis incomplete and dextrin units remain. Primary sources of β- Amylase are the seeds of higher plants and sweet potatoes. During ripening of fruits, β-Amylase breaks down starch into maltose resulting in the sweetness of ripened fruit. In the industry it is used for fermentation in brewing and distilling industry. 3. γ – Amylase γ-Amylase (EC 3.2.1.3 ) cleaves α(1-6)glycosidic linkages, in addition to cleaving the last α(1- 4)glycosidic linkages at the nonreducing end of amylose and amylopectin, unlike the other forms of amylase, yielding glucose. γ- amylase is most efficient in acidic environments and has an optimum pH of 3. Sources of amylase a-Amylases are universally distributed throughout the plant, animal, and microbial kingdoms. The enzymes from microbial sources have dominated applications in industrial processes. Table: Sources of amylases Source Example Plant Family 1 a-amylases, Family 2 a-amylases and Family 3 a-amylases from various monocotyledons, dicotyledons, and gymnosperms. Bacteria Bacillus, Brevibacterium, Clostridium, Halomonas, Naxibacter, Nesterenkonia, Paenibacillus, Pseudomonas, Streptomyces sp. Bacillus subtilis, Bacillus stearothermophilus, Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus acidocaldarius, Bifidobacterium bifidum, Bifidobacterium acerans, B. licheniformis, and Bacillus halodurans, Anoxybacillus beppuensis, Bacillus laterosporus, Bacillus acidicola, Chryseobacterium taeanense, Clostridium sp. Microbacterium foliorum, Nesterenkonia sp, Thermococcus sp, Anoxybacillus
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  flavithermus Fungi Acremonium, Aspergillus,Penicillium, Mucor, Neurospora, and Thermomyces sp. Aspergillus niger, Aspergillus flavus, Aspergillus oryzae, Thermomyces lanuginosus Strain improvement is done to increase production as well as to improve the properties of the amylases enzyme. The catalytic properties of amylases are determined by their 3-D structure. Hence, enzyme properties can be altered by site-directed mutagenesis. Using this method, the properties of an enzyme can be improved, by making it thermostable, reducing its dependence on cofactors, or increasing its activity at low temperature. Studies on the cloning of the a-amylase gene have been extensively carried out for hyperproduction. Below table shows some strategies to improve the amylase activity Table: Strain Improvement for amylases
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  Mode of actionof amylases Several aspects of amylase mode of action can be distinguished. A first aspect deals with the action mechanism, i.e. the hydrolysis of the glucosidic bond on a molecular scale. All the enzymes of GH family 13 retain the anomeric configuration and work according to the double displacement mechanism. This is an acid-base catalysed reaction, requiring a proton donor and a nucleophile, in which a glycosyl-enzyme intermediate is formed Typically, all endo-acting amylases work according to this action mechanism. In contrast, exo-acting amylases, such as β- amylases, are inverting amylases and work through the single displacement mechanism The reaction proceeds through an oxocarbenium ion-like transition state. Another aspect of amylase mode of action is that several models for amylase action pattern have been proposed, such as the random action and the multiple attack action. Schematic representation of amylase action patterns is given in figure below.  Random manner it is believed that α-amylases degrade the starch polymers in a random manner. This has also been referred to as a single attack or multi-chain attack action. This mode of action implies that all bonds are equally susceptible to hydrolysis. As a result, a rapid decrease in starch polymer MW can be observed.  Multiple attack action Amylases with a multiple attack action cleave several glycosidic bonds successively after the first (random) hydrolytic attack before dissociating from the substrate. The multiple attack action is an intermediate between the single-chain and the multichain (or random) action. Multiple attact action is defined as the degree of multiple attack (DMA) as the number of bonds broken
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  during the lifetimeof an enzyme-substrate complex minus one (i.e. the initial random cleavage). The multiple attack action is often referred to by the more generic term “processivity” Figure: Schematic representation of amylase action patterns
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  Applications of a-Amylase a-Amylaseshave very wide range of biotechnological applications in the textile, food, pharmaceutical, detergent and various other industries. Due to latest developments in biotechnology, the applications of a-amylases have been widened to other fields like clinical, medicinal, and analytical chemistry. Application of Amylases Detergent Industry Textile Desizing Mecinial & clinical chemistry Paper Industry Strach liquefication Scarification Bread & Baking Industry Alcohol Production Glucose & frutose production
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  References: Bijttebier, A., Goesaert,H., & Delcour, J. (2008). Amylase action pattern on starch polymers. Biologia, 63(6), 989-999. Sundarram, A., & Murthy, T. P. K. (2014). α-amylase production and applications: a review. Journal of Applied & Environmental Microbiology, 2(4), 166-175. Pandey, A., Negi, S., & Soccol, C. R. (Eds.). (2016). Current Developments in Biotechnology and Bioengineering: Production, Isolation and Purification of Industrial Products. Elsevier.