Amylase: Characteristics, Classification, Structure, Functions

Amylase is the term used to identify an important group of enzymes that is responsible for the hydrolysis of glycosidic bonds between glucose molecules present in carbohydrates, such as starch and other related ones, which are ingested in the diet of many living organisms.

This type of enzyme is produced by bacteria, fungi, animals and plants, where they catalyze basically the same reactions and have various functions, mainly related to energy metabolism.

Graphic representation of an Alpha Amylase of animal origin (Source: Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute [Public domain] via Wikimedia Commons)

The products of the hydrolysis reactions of the glycosidic bonds can be considered as characteristic for each type of amylolytic enzyme, so this is often an important parameter for their classification.

The importance of these enzymes, anthropocentrically speaking, is not only physiological, since at present this type of enzymes has great biotechnological significance in the industrial production of food, paper, textiles, sugars and others.

The term “amylase” derives from the Greek ” amylon “, which means starch, and was coined in 1833 by scientists Payen and Persoz, who studied the hydrolytic reactions of this enzyme on starch.

Article index

  • one

    Characteristics

    • 1.1

      Substrate characteristics

  • two

    Classification

    • 2.1

      Current ranking

  • 3

    Features

    • 3.1

      In animals

    • 3.2

      In the plants

    • 3.3

      In microorganisms

    • 3.4

      Industrial uses

  • 4

    References

Characteristics

Some amylases are multimeric in nature, such as sweet potato β-amylase, which behaves like a tetramer. However, the approximate molecular weight of the amylase monomers is in the range of 50 kDa.

In general, both plant and animal enzymes have a relatively “common” amino acid composition and have optimal activities at pH between 5.5 and 8 units (with animal amylases being more active at more neutral pH).

Amylases are enzymes capable of hydrolyzing glycosidic bonds of a large number of polysaccharides, generally producing disaccharides, but they are not capable of hydrolyzing complexes such as cellulose.

Substrate characteristics

The reason why amylases are so important in nature, especially in the digestion of carbohydrates, is related to the ubiquitous presence of their natural substrate (starch) in the tissues of “higher” vegetables, which serve as a source. of food for multiple types of animals and microorganisms.

This polysaccharide is composed, in turn, of two macromolecular complexes known as amylose (insoluble) and amylopectin (soluble). The amylose moieties are made up of linear chains of glucose residues linked by α-1,4 bonds and are degraded by α-amylases.

Amylopectin is a high molecular weight compound, it is made up of branched chains of glucose residues linked by α-1,4 bonds, whose branches are supported by α-1,6 bonds.

Classification

Amylase enzymes are classified according to the site where they are capable of breaking glycosidic bonds as endoamylases or exoamylases. The former hydrolyze bonds in internal regions of carbohydrates, while the latter can only catalyze the hydrolysis of residues at the ends of polysaccharides.

Furthermore, the traditional classification is related to the stereochemistry of their reaction products, so these proteins with enzymatic activity are also classified as α-amylases, β-amylases or γ-amylases.

-The α-amylases (α-1,4-glucan 4-glucan hydrolases) are endoamylases that act on internal bonds of linear conformation substrates and whose products have α configuration and are mixtures of oligosaccharides.

-The β-amylases (α-1,4-glucan maltohydrolases) are plant exoamylases that act on bonds at the non-reducing ends of polysaccharides such as starch and whose hydrolytic products are residues of β-maltose.

-Finally, γ-amylases are a third class of amylases also called glucoamylases (α-1,4-glucan glucohydrolases) which, like β-amylases, are exoamylases capable of removing single glucose units from non-reducing ends of the polysaccharides and invert their configuration.

The latter class of enzymes can hydrolyze both α-1,4 and α, 1-6 bonds, converting substrates such as starch to D-glucose. In animals they are found mainly in liver tissue.

Current ranking

With the advent of new biochemical analysis techniques for both enzymes and their substrates and products, certain authors have determined that there are at least six classes of amylase enzymes:

1-Endoamylases that hydrolyze α-1,4 glucosidic bonds and can “bypass” ( bypass) α-1,6 bonds. Examples of this group are α-amylases.

2-Exoamylases capable of hydrolyzing α-1,4, the main products of which are maltose residues and the α-1,6 bonds cannot be “skipped”. Example of the group are β-amylases.

3-Exoamylases capable of hydrolyzing α-1,4 and α-1,6 bonds, such as amyloglucosidases (glucoamylases) and other exoamylases.

 4-Amylases that only hydrolyze α-1,6 glucosidic bonds. In this group are “debranching” enzymes and others known as pullulanases.

5-Amylases such as α-glucosidases, which preferentially hydrolyze α-1,4 bonds of short oligosaccharides produced by the action of other enzymes on substrates such as amylose or amylopectin.

6-Enzymes that hydrolyze starch to non-reducing cyclic polymers of D-glucosidic residues known as cyclodextrins, such as some bacterial amylases.

Features

Many are the functions that are attributed to the enzymes with amylase activity, not only from the natural or physiological point of view, but also from the commercial and industrial point of view, directly related to man.

In animals

Amylases in animals are essentially present in saliva, liver and pancreas, where they mediate the degradation of the different polysaccharides consumed in the diet (of animal origin (glycogens) or vegetable (starches)).

The α-amylase present in saliva is used as an indicator of the physiological state of the salivary glands, since it constitutes more than 40% of the protein production of these glands.

In the oral compartment, this enzyme is responsible for the “pre-digestion” of starch, producing residues of maltose, maltotriose and dextrin.

In the plants

In plants, starch is a reserve polysaccharide and its hydrolysis, mediated by amylase enzymes, has many important functions. Among them the following can be highlighted:

  • Germination of cereal seeds by digestion of the aleurone layer.
  • The degradation of reserve substances for the acquisition of energy in the form of ATP.

In microorganisms

Many microorganisms use amylases to obtain carbon and energy from various sources of polysaccharides. In industry, these microorganisms are exploited for the large-scale production of said enzymes, which serve to satisfy different commercial demands of man.

Industrial uses

In industry, amylases are used for various purposes, including the manufacture of maltose, high fructose syrups, oligosaccharide mixtures, dextrins, etc.

They are also used for the direct alcoholic fermentation of starch to ethanol in the brewing industry, and for the use of waste water produced during the processing of plant-based foods as a food source for the growth of microorganisms, for example.

References

  1. Aiyer, PV (2005). Amylases and their applications. African Journal of Biotechnology , 4 (13), 1525–1529.
  2. Azcón-Bieto, J., & Talón, M. (2008). Fundamentals of Plant Physiology (2nd ed.). Madrid: McGraw-Hill Interamericana of Spain.
  3. Del Vigna, P., Trinidade, A., Naval, M., Soares, A., & Reis, L. (2008). Saliva Composition and Functions: A comprehensive review. The Journal of Contemporary Dental Practice , 9 (3), 72–80.
  4. Naidu, MA, & Saranraj, P. (2013). Bacterial Amylase: A Review. International Journal of Pharmaceutical & Biological Archives , 4 (2), 274–287.
  5. Salt, W., & Schenker, S. (1976). Amylase- Its clinical significance: a Review of the Literature. Medicine , 55 (4), 269–289.
  6. Saranraj, P., & Stella, D. (2013). Fungal Amylase – A Review. International Journal of Microbiological Research , 4 (2), 203–211.
  7. Solomon, E., Berg, L., & Martin, D. (1999). Biology (5th ed.). Philadelphia, Pennsylvania: Saunders College Publishing.
  8. Thoma, JA, Spradlin, JE, & Dygert, S. (1925). Plant and Animal Amylases. Ann. Chem. , 1 , 115-189.

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