From Proteopedia

Revision as of 20:28, 30 March 2010

Shane Riley α-Amylase Template:STRUCTURE 1hvx

Introduction

Amylase is the first enzyme to be discovered. It was discovered and isolated by Anselme Payen in 1833. Amylases are hydrolases, acting on on α-1,4-glycosidic bonds^[1]Cite error: Invalid <ref> tag; refs with no name must have content. Amylases can be further subdivided into α,β and γ amylases. α-Amylase is an enzyme that acts as a catalyst for the hydrolysis of alpha-linked polysaccharides into α-anomeric products.^[2] The enzyme can be derived from a variety of sources, each with different characteristics. α-Amylase found within in the human body serves as the enzyme active in pancreatic juice and salvia. α-Amylase is not only essential in human physiology but have a number of important biotechnological functions in various processing industries. ^[3]

References

1. ↑ Aghajari N, Feller G, Gerday C, Haser R. Crystal structures of the psychrophilic alpha-amylase from Alteromonas haloplanctis in its native form and complexed with an inhibitor. Protein Sci. 1998 Mar;7(3):564-72. PMID:9541387
2. ↑ Suvd D, Fujimoto Z, Takase K, Matsumura M, Mizuno H. Crystal structure of Bacillus stearothermophilus alpha-amylase: possible factors determining the thermostability. J Biochem. 2001 Mar;129(3):461-8. PMID:11226887
3. ↑

   Structure

   BSTA comprises of a single polypeptide chain <ref></ref> . This chain is folded into three domains A, B and C. These domains are generally recognized on α-amylase enzymes. The constitutes the core structure, with a (β/α)barrel.The consists of a sheet of four anti-parallel β-strands with a pair of anti-parallel β-strands. Long loops are observed between the β-strands. Located within the B domain is the for Ca²⁺-Na⁺-Ca²⁺.consisting of eight β-strands assembles into a globular unit forming a Greek key motif. It also holds the Ca²⁺ binding site in association with domain A.Positioned on the C-terminal side of the β-strands of the (β/α)barrel in domain A, is the active site. The catalytic residues involved in the active site are Asp234, Glu264, and Asp331, for BSTA. The residues are identical to other α-amylases, yet there are positional differences which reflect the flexible nature of catalytic resides. found in the interior of domain B and at the interface of domain A and C, constitute the metal ion binding sites. CaI is consistent in all α-amylases, however there are structural differences between the linear trio of CaI, CaII and Na in other enzymes.CaIII acts as a bridge between two loops, one from Aα6 of domain A, and between Cβ1 and Cβ2 of domain C.

   Function

   In the human body α-amylase is part of digestion with the breakdown of carbohydrates in the diet. Salivary α-Amylase found in saliva, hydrolyzes the (α1-4) glycosidic linkages of starch seperating it into short polysaccharide fragments. Once the enzyme reaches the stomach it becomes inactivated due to the acidic pH. Further breakdown of starch occurs by secretion of a second form of the enzyme by the pancreas. Pancreatic juice enters the duodenum and pancreatic α-amylase further cleaves starch to yield maltose, maltotriose and oligosaccharides referred to as dextrins, which are fragments of amylopectin consisting of (α1-6)branch points. Microvilli of the intestinal epithelia break maltose and dextrins into glucose, which absorbs into the circulatory system. Glycogen has a relatively similar structure as starch, and thus proceeds in the same digestive pathway.

   Regulation of α-amylase is done through a number of inhibitors. These inhibitors are classified according to six categories, based on their tertiary structures. Inhibitors of α-amylase block the active site of the enzyme at different sites. In animals, inhibitors control the conversion of starch to simple sugars during glucose peaks after a meal, so that it occurs at a rate the body can handle. This is particularly important for diabetics, who require low quantities of α-amylase to maintain control over glucose levels. However after taking insulin, pancreatic α-amylase escalates. Plants use these inhibitors as a defence mechanism that inhibits use of α-amylase in insects, thus protecting from breakdown.

   Industrial Uses

   Alpha amylase is used extensively in many various industrial processes. In textile weaving, starch is added for warping. After weaving, the starch is then later removed by through Bacillus subtilis α-amylase. Dextrin, a viscosity improver, filler or ingredient of food is manufactured by the liquefaction of starch by bacteria α-amylase. Bacterial α-amylases of B.subtilis, or B.licheniformis is used for the initial starch liquefaction in producing high conversion glucose syrup. Pancreatitis can be tested by determining the level of amylases in the blood, as result of damaged amylase-producing cells, or excretion due to renal failure.α-Amylase is used for the production of malt, as the enzyme is produced during the germination of cereal grains. texttext

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