Main Difference – Alpha vs Beta Amylase
The action of amylase enzyme can hydrolyze starch into sugar units. Amylase is naturally present in saliva and pancreatic of humans and some other mammals, where it initiates the biochemical process of food bolus digestion. During oral digestion, starch foods (rice, bread, yams and potatoes), give a somewhat sweet taste because salivary amylase degrades some of their starch into sugar. Amylase was first discovered and isolated by Anselme Payen in 1833. Amylase enzymes are specifically named by different Greek letters including Alpha (α)-Amylase, beta (β)-Amylase and gamma (γ)-Amylase. All these enzymes are glycoside hydrolases and act on α-1,4-glycosidic bonds. Alpha (α)-Amylase is considered to be a major digestive enzyme whereas beta (β)-amylase is considered to be a major enzyme involved in seed germination and fruit ripening. But compared to beta (β)-Amylase and gamma (γ)-Amylase, the α-amylases (EC 3.2.1.1) are calcium metalloenzymes, and they are not capable of functioning in the absence of calcium. This is the main difference between Alpha and Beta Amylase. However, both Alpha and beta amylases are used commercially in fermentation processes such as brewing beer and liquor prepared from sugars derived from starch. In this article, let’s further elaborate what are the differences between Alpha and Beta Amylase.
This article covers,
1. What is Alpha Amylase? – Definition, Functions, Properties, and Characteristics
2. What is Beta Amylase? – Definition, Functions, Properties, and Characteristics
3. What is the difference between Alpha and Beta Amylase? – Comparison of physical and functional characteristics
What is Alpha Amylase
Alpha Amylase is considered as a major digestive enzyme in the mammalian digestive tract. The human salivary and pancreatic amylases are α-amylases and plants, fungi (ascomycetes and basidiomycetes) and bacteria (Bacillus) can also produce α-amylases.
The optimum pH of Alpha Amylase is 6.7–7.0. Calcium is essential the functioning of α-amylases; hence it is known as a calcium metalloenzyme. Alpha amylase can break down long-chain carbohydrates such as starch amylose into maltotriose and maltose or amylopectin into maltose, glucose and limit dextrin.
Ribbon diagram of human salivary alpha-amylase
What is Beta Amylase
Beta amylase is mainly produced by bacteria, fungi, and plants and it catalyzes the enzymatic breakdown of the second α-1,4 glycosidic bond of non-reducing sugars, thereby cleaving off maltose at a time. β-amylase breaks starch into maltose, causing the sweet flavor of ripe fruit. The optimum pH for the functioning of β-amylase is 4.0–5.0. Animals do not produce β-amylase.
Ribbon diagram of barley beta-amylase
Difference Between Alpha and Beta Amylase
Alpha and Beta Amylase have significantly different physical and functional characteristics. These can be categorized into following subgroups,
Alternative Names
Alpha Amylase: 1,4-α-D-glucan glucanohydrolase and glycogenase are alternative names for α-amylase.
Beta Amylase:1,4-α-D-glucan maltohydrolase, glycogenase, and saccharogen amylase are alternative names for β-amylase.
EC number
Alpha Amylase: EC 3.2.1.1
Beta Amylase: EC 3.2.1.2
Production
Alpha Amylase: Mammalian digestive system can synthesize α-amylase; thus human salivary and pancreatic amylases are α-amylases. In addition, α–amylases can be produced by plants, fungi (ascomycetes and basidiomycetes) and bacteria (Bacillus).
Beta Amylase: β-amylase is produced by bacteria, fungi, and plants. Tissues or cells of animal cannot produce β-amylase, even though it may exist in microorganisms present within the digestive tract.
Role of Calcium
Alpha Amylase: Calcium is essential for the functioning of α-amylases and hence it is known as a calcium metallo-enzyme.
Beta Amylase: Calcium is not required for the functioning of β-amylases.
Optimum pH
Alpha Amylase: The optimum pH for β-amylase is 6.7–7.0
Beta Amylase: The optimum pH for β-amylase is 4.0–5.0
Major Function
Alpha Amylase: α-amylase is mainly involved in the food digestion process.
Beta Amylase: β-amylase is mainly involved in the fruit ripening and seed germination process.
Acting Site
Alpha Amylase: α-amylase can act anywhere on the substrate.
Beta Amylase: β-amylase can act from the non-reducing end, and catalyzes the hydrolysis of the second α-1,4 glycosidic bond
Major outcomes of the enzymatic reactions
Alpha Amylase: Long-chain carbohydrates (amylose and amylopectin strands) can be broken down by α-amylase and give maltotriose and maltose from amylose, or maltose, glucose and limit dextrin from amylopectin
Beta Amylase: During fruit ripening process, starch is broken down by β-amylase into maltose, causing in the sweet flavor of ripe fruit.
Rate of Reaction
Alpha Amylase: α-amylase have a tendency to be faster-acting than β-amylase.
Beta Amylase: β-amylase have a tendency to be slower-acting than α-amylase.
Physical and Chemical Properties
Alpha Amylase: α-amylase is insensitive to high temperatures and heavy metal ions and is inactivated at a low pH.
Beta Amylase: β-amylase is sensitive to high temperatures and heavy metal ions, and is stable at a low pH.
In conclusion, amylase is an enzyme that can hydrolyze starch into smaller molecules. But α-amylase requires Ca2+ for activity and yield glucose, maltotriose, and maltose as end products. In contrast, β-amylase does not require Ca2+ and hydrolyzes soluble starch or amylose, yielding only maltose as an end product.
References
Frydenberg, O and G. Nielsen. 1965. Amylase isozymes in germinating barley seeds. Hereditas 54: 123-129.
Onckelen, H. A. and R. Verbeek. 1969. Formation of a-amylase isozymes during germination of barley. Planta 88: 255-260.
Rejzek, M.; Stevenson, C. E.; Southard, A. M.; Stanley, D.; Denyer, K.; Smith, A. M.; Naldrett, M. J.; Lawson, D. M.; Field, R. A. (2011). “Chemical genetics and cereal starch metabolism: Structural basis of the non-covalent and covalent inhibition of barley β-amylase”. Molecular BioSystems. 7 (3): 718–730.
Image Courtesy:
“Salivary alpha-amylase 1SMD” – From PDB entry 1SMD – Own work (Public Domain) via Commons Wikimedia
“2xfr b amylase” By A2-33 – Own work (CC BY-SA 3.0) via Commons Wikimedia
