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Amylase

The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform

Birte Svensson – 1st expert on this subject based on the ideXlab platform

  • α-Amylase: an enzyme specificity found in various families of glycoside hydrolases
    Cellular and Molecular Life Sciences, 2014
    Co-Authors: Stefan Janecek, Birte Svensson, E. Ann Macgregor

    Abstract:

    α-Amylase (EC 3.2.1.1) represents the best known amylolytic enzyme. It catalyzes the hydrolysis of α-1,4-glucosidic bonds in starch and related α-glucans. In general, the α-Amylase is an enzyme with a broad substrate preference and product specificity. In the sequence-based classification system of all carbohydrate-active enzymes, it is one of the most frequently occurring glycoside hydrolases (GH). α-Amylase is the main representative of family GH13, but it is probably also present in the families GH57 and GH119, and possibly even in GH126. Family GH13, known generally as the main α-Amylase family, forms clan GH-H together with families GH70 and GH77 that, however, contain no α-Amylase. Within the family GH13, the α-Amylase specificity is currently present in several subfamilies, such as GH13_1, 5, 6, 7, 15, 24, 27, 28, 36, 37, and, possibly in a few more that are not yet defined. The α-Amylases classified in family GH13 employ a reaction mechanism giving retention of configuration, share 4–7 conserved sequence regions (CSRs) and catalytic machinery, and adopt the (β/α)_8-barrel catalytic domain. Although the family GH57 α-Amylases also employ the retaining reaction mechanism, they possess their own five CSRs and catalytic machinery, and adopt a (β/α)_7-barrel fold. These family GH57 attributes are likely to be characteristic of α-Amylases from the family GH119, too. With regard to family GH126, confirmation of the unambiguous presence of the α-Amylase specificity may need more biochemical investigation because of an obvious, but unexpected, homology with inverting β-glucan-active hydrolases.

  • structure specificity and function of cyclomaltodextrinase a multispecific enzyme of the α Amylase family
    Biochimica et Biophysica Acta, 2000
    Co-Authors: Kwan-hwa Park, Taekyou Cheong, Byungha Oh, Birte Svensson

    Abstract:

    Abstract Cyclomaltodextrinase (CDase, EC 3.2.1.54), maltogenic Amylase (EC 3.2.1.133), and neopullulanase (EC 3.2.1.135) are reported to be capable of hydrolyzing all or two of the following three types of substrates: cyclomaltodextrins (CDs); pullulan; and starch. These enzymes hydrolyze CDs and starch to maltose and pullulan to panose by cleavage of α-1,4 glycosidic bonds whereas α-Amylases essentially lack activity on CDs and pullulan. They also catalyze transglycosylation of oligosaccharides to the C3-, C4- or C6-hydroxyl groups of various acceptor sugar molecules. The present review surveys the biochemical, enzymatic, and structural properties of three types of such enzymes as defined based on the substrate specificity toward the CDs: type I, cyclomaltodextrinase and maltogenic Amylase that hydrolyze CDs much faster than pullulan and starch; type II, Thermoactinomyces vulgaris Amylase II (TVA II) that hydrolyzes CDs much less efficiently than pullulan; and type III, neopullulanase that hydrolyzes pullulan efficiently, but remains to be reported to hydrolyze CDs. These three types of enzymes exhibit 40–60% amino acid sequence identity. They occur in the cytoplasm of bacteria and have molecular masses from 62 to 90 kDa which are slightly larger than those of most α-Amylases. Multiple amino acid sequence alignment and crystal structures of maltogenic Amylase and TVA II reveal the presence of an N-terminal extension of approximately 130 residues not found in α-Amylases. This unique N-terminal domain as seen in the crystal structures apparently contributes to the active site structure leading to the distinct substrate specificity through a dimer formation. In aqueous solution, most of these enzymes show a monomer–dimer equilibrium. The present review discusses the multiple specificity in the light of the oligomerization and the molecular structures arriving at a clarified enzyme classification. Finally, a physiological role of the enzymes is proposed.

  • Protein engineering in the α-Amylase family: catalytic mechanism, substrate specificity, and stability
    Plant Molecular Biology, 1994
    Co-Authors: Birte Svensson

    Abstract:

    Most starch hydrolases and related enzymes belong to the α-Amylase family which contains a characteristic catalytic (β/α)_8-barrel domain. Currently known primary structures that have sequence similarities represent 18 different specificities, including starch branching enzyme. Crystal structures have been reported in three of these enzyme classes: the α-Amylases, the cyclodextrin glucanotransferases, and the oligo-1,6-glucosidases. Throughout the α-Amylase family, only eight amino acid residues are invariant, seven at the active site and a glycine in a short turn. However, comparison of three-dimensional models with a multiple sequence alignment suggests that the diversity in specificity arises by variation in substrate binding at the β→α loops. Designed mutations thus have enhanced transferase activity and altered the oligosaccharide product patterns of α-Amylases, changed the distribution of α-, β- and γ-cyclodextrin production by cyclodextrin glucanotransferases, and shifted the relative α-1,4:α-1,6 dual-bond specificity of neopullulanase. Barley α-Amylase isozyme hybrids and Bacillus α-Amylases demonstrate the impact of a small domain B protruding from the (β/α)_8-scaffold on the function and stability. Prospects for rational engineering in this family include important members of plant origin, such as α-Amylase, starch branching and debranching enzymes, and amylomaltase.

Michael J Gidley – 2nd expert on this subject based on the ideXlab platform

  • effects of processing high amylose maize starches under controlled conditions on structural organisation and Amylase digestibility
    Carbohydrate Polymers, 2009
    Co-Authors: Aung K Htoon, Ashok K Shrestha, Bernadine M Flanagan, Amparo Lopezrubio, Anthony R Bird, Elliot P Gilbert, Michael J Gidley

    Abstract:

    The Amylase digestibility of high-amylose maize starches has been compared before and after thermomechanical processing. Starches were analysed for enzyme-resistant starch yield, apparent amylose content, crystallinity (X-ray diffraction), and molecular order (NMR and FTIR), both before and after treatment with a-Amylase. All samples had significant (>10%) enzyme-resistant starch levels irrespective of the type and extent of thermal or enzymic processing. Molecular or crystalline order was not a pre-requisite for enzyme resistance. Near-amorphous forms of high amylose maize starches are likely to undergo recrystallisation during the enzyme-digestion process. The mechanism of enzyme resistance of granular high-amylose starches is found to be qualitatively different to that for processed high-amylose starches. For all samples, measured levels of enzyme resistance are due to the interruption of a slow digestion process, rather than the presence of completely indigestible material. 2008 Elsevier Ltd. All rights reserved.

Ashok K Shrestha – 3rd expert on this subject based on the ideXlab platform

  • effects of processing high amylose maize starches under controlled conditions on structural organisation and Amylase digestibility
    Carbohydrate Polymers, 2009
    Co-Authors: Aung K Htoon, Ashok K Shrestha, Bernadine M Flanagan, Amparo Lopezrubio, Anthony R Bird, Elliot P Gilbert, Michael J Gidley

    Abstract:

    The Amylase digestibility of high-amylose maize starches has been compared before and after thermomechanical processing. Starches were analysed for enzyme-resistant starch yield, apparent amylose content, crystallinity (X-ray diffraction), and molecular order (NMR and FTIR), both before and after treatment with a-Amylase. All samples had significant (>10%) enzyme-resistant starch levels irrespective of the type and extent of thermal or enzymic processing. Molecular or crystalline order was not a pre-requisite for enzyme resistance. Near-amorphous forms of high amylose maize starches are likely to undergo recrystallisation during the enzyme-digestion process. The mechanism of enzyme resistance of granular high-amylose starches is found to be qualitatively different to that for processed high-amylose starches. For all samples, measured levels of enzyme resistance are due to the interruption of a slow digestion process, rather than the presence of completely indigestible material. 2008 Elsevier Ltd. All rights reserved.