Enzymes, Starch Conversion

Bentley, Ian S

doi:10.1002/0471250589.ebt088

Cited by 7 publications

(9 citation statements)

References 6 publications

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“…During liquefaction, starch granules are gelatinized in a jet cooker at 105 to 110°C for 5 min in aqueous solution (pH 5.8 to 6.5) and then partially hydrolyzed at ␣-1,4 During saccharification (which runs for 24 to 72 h), the liquefied starch is converted into low-molecular-weight saccharides and ultimately into glucose or maltose. Glucose syrups (up to 95 to 96% glucose) are produced using pullulanase and glucoamylase in combination, while maltose syrups (up to 80 to 85% maltose) are produced using pullulanase and ␤-amylase (25,69). The natural pH of the starch slurry is approximately 4.5.…”

Section: Applications In Starch Processingmentioning

confidence: 99%

Hyperthermophilic Enzymes: Sources, Uses, and Molecular Mechanisms for Thermostability

Vieille¹,

Zeikus

2001

Microbiol Mol Biol Rev

1,847

1,476

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Enzymes synthesized by hyperthermophiles (bacteria and archaea with optimal growth temperatures of >80°C), also called hyperthermophilic enzymes, are typically thermostable (i.e., resistant to irreversible inactivation at high temperatures) and are optimally active at high temperatures. These enzymes share the same catalytic mechanisms with their mesophilic counterparts. When cloned and expressed in mesophilic hosts, hyperthermophilic enzymes usually retain their thermal properties, indicating that these properties are genetically encoded. Sequence alignments, amino acid content comparisons, crystal structure comparisons, and mutagenesis experiments indicate that hyperthermophilic enzymes are, indeed, very similar to their mesophilic homologues. No single mechanism is responsible for the remarkable stability of hyperthermophilic enzymes. Increased thermostability must be found, instead, in a small number of highly specific alterations that often do not obey any obvious traffic rules. After briefly discussing the diversity of hyperthermophilic organisms, this review concentrates on the remarkable thermostability of their enzymes. The biochemical and molecular properties of hyperthermophilic enzymes are described. Mechanisms responsible for protein inactivation are reviewed. The molecular mechanisms involved in protein thermostabilization are discussed, including ion pairs, hydrogen bonds, hydrophobic interactions, disulfide bridges, packing, decrease of the entropy of unfolding, and intersubunit interactions. Finally, current uses and potential applications of thermophilic and hyperthermophilic enzymes as research reagents and as catalysts for industrial processes are described

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Section: Applications In Starch Processingmentioning

confidence: 99%

Hyperthermophilic Enzymes: Sources, Uses, and Molecular Mechanisms for Thermostability

Vieille¹,

Zeikus

2001

Microbiol Mol Biol Rev

1,847

1,476

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“…The potential use of biocatalysts at high temperatures for technological purposes has drawn interest in developing thermoactive and thermostable enzymes that would provide significant processing advantages [14]. For example, thermostable xylose isomerases (XIs) (EC 5.3.1.5), which catalyze the isomerization of d ‐xylose to d ‐xylulose in vivo , are used for the conversion of d ‐glucose into d ‐fructose for the production of high‐fructose corn syrup [15]. Elevated bioprocessing temperatures are preferred to achieve higher catalytic rates as well as more favorable equilibrium yields [16].…”

Section: Amino‐acid Content Of the Total Proteins Of Selected Mesophmentioning

confidence: 99%

Bivalent cations and amino‐acid composition contribute to the thermostability of Bacillus licheniformis xylose isomerase

Vieille

Epting

Kelly

et al. 2001

European Journal of Biochemistry

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Comparative analysis of genome sequence data from mesophilic and hyperthermophilic micro-organisms has revealed a strong bias against specific thermolabile aminoacid residues (i.e. N and Q) in hyperthermophilic proteins. The N þ Q content of class II xylose isomerases (XIs) from mesophiles, moderate thermophiles, and hyperthermophiles was examined. It was found to correlate inversely with the growth temperature of the source organism in all cases examined, except for the previously uncharacterized XI from Bacillus licheniformis DSM13 (BLXI), which had an N þ Q content comparable to that of homologs from much more thermophilic sources. To determine whether BLXI behaves as a thermostable enzyme, it was expressed in Escherichia coli, and the thermostability and activity properties of the recombinant enzyme were studied. Indeed, it was optimally active at 70-72 8C, which is significantly higher than the optimal growth temperature (37 8C) of B. licheniformis. The kinetic properties of BLXI, determined at 60 8C with glucose and xylose as substrates, were comparable to those of other class II XIs. The stability of BLXI was dependent on the metallic cation present in its two metal-binding sites. The enzyme thermostability increased in the order apoenzyme , Mg 2þ -enzyme , Co 2þ -enzyme < Mn 2þ -enzyme, with melting temperatures of 50.3 8C, 53.3 8C, 73.4 8C, and 73.6 8C. BLXI inactivation was first-order in all conditions examined. The energy of activation for irreversible inactivation was also strongly influenced by the metal present, ranging from 342 kJ·mol 21 (apoenzyme) to 604 kJ·mol 21 (Mg 2þ -enzyme) to 1166 kJ·mol 21 (Co 2þ -enzyme). These results suggest that the first irreversible event in BLXI unfolding is the release of one or both of its metals from the active site. Although N þ Q content was an indicator of thermostability for class II XIs, this pattern may not hold for other sets of homologous enzymes. In fact, the extremely thermostable a-amylase from B. licheniformis was found to have an average N þ Q content compared with homologous enzymes from a variety of mesophilic and thermophilic sources. Thus, it would appear that protein thermostability is a function of more complex molecular determinants than amino-acid content alone.Keywords: Bacillus licheniformis; metal binding; thermostability; xylose isomerase.It has become apparent that protein thermostability arises not from a single chemical or physical factor, but from numerous subtle contributions integrated over the entire molecular structure [1 -6]. Thermostable proteins usually exhibit no significant differences in backbone conformation when compared with less thermostable proteins, but they typically have increased numbers of salt bridges, side chain-side chain hydrogen bonds, and residues involved in a helices [7 -9]. Stability at very high temperatures further requires that a particular enzyme resist thermally induced deleterious chemical reactions, which usually occur at insignificant rates at lower temperatures [10]. For example, one of the mos...

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“…The major use of starch in the food industry is for the production of glucose, glucose syrups, and high-fructose corn syrups. In addition, the resulting glucose can be utilized to produce other products, such as ethanol, amino acids, or organic acids (2).…”

mentioning

confidence: 99%

Properties of a Novel Thermostable Glucoamylase from the Hyperthermophilic Archaeon Sulfolobus solfataricus in Relation to Starch Processing

Kim

Park

Kim

et al. 2004

Appl Environ Microbiol

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A gene (ssg) encoding a putative glucoamylase in a hyperthermophilic archaeon, Sulfolobus solfataricus, was cloned and expressed in Escherichia coli, and the properties of the recombinant protein were examined in relation to the glucose production process. The recombinant glucoamylase was extremely thermostable, with an optimal temperature at 90°C. The enzyme was most active in the pH range from 5.5 to 6.0. The enzyme liberated ␤-D-glucose from the substrate maltotriose, and the substrate preference for maltotriose distinguished this enzyme from fungal glucoamylases. Gel permeation chromatography and sedimentation equilibrium analytical ultracentrifugation analysis revealed that the enzyme exists as a tetramer. The reverse reaction of the glucoamylase from S. solfataricus produced significantly less isomaltose than did that of industrial fungal glucoamylase. The glucoamylase from S. solfataricus has excellent potential for improving industrial starch processing by eliminating the need to adjust both pH and temperature.

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Enzymes, Starch Conversion

Cited by 7 publications

References 6 publications

Hyperthermophilic Enzymes: Sources, Uses, and Molecular Mechanisms for Thermostability

Hyperthermophilic Enzymes: Sources, Uses, and Molecular Mechanisms for Thermostability

Bivalent cations and amino‐acid composition contribute to the thermostability of Bacillus licheniformis xylose isomerase

Properties of a Novel Thermostable Glucoamylase from the Hyperthermophilic Archaeon Sulfolobus solfataricus in Relation to Starch Processing

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