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Jan A. Delcour - One of the best experts on this subject based on the ideXlab platform.
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Hydrolysis of amylopectin by amylolytic enzymes: structural analysis of the residual amylopectin population.
Carbohydrate Research, 2009Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:Abstract Amylopectin fine structures were studied following limited hydrolysis of gelatinised waxy maize starch by amylases with a different level of inner chain Attack (LICA). This was done by size exclusion chromatography as well as by debranching the (partially hydrolysed) amylopectin samples and studying the size distributions of the released chains. α-Amylases from Bacillus amyloliquefaciens and Aspergillus oryzae , with a relatively high LICA, drastically altered amylopectin chain length distribution and reduced the amylopectin molecular size (MS) significantly even at a low to moderate degree of hydrolysis (DH). Porcine pancreatic α-amylase (PPA), with a rather low LICA but a high multiple Attack Action on amylose, reduced the amylopectin MS much slower. Following hydrolysis by PPA to a DH of 10% and enzymic debranching of the amylopectin residue, several subpopulations of chains consisting of 2–12 glucose units were detected, indicating a multiple Attack Action on the amylopectin side chains. During the early stages of hydrolysis, the maltogenic Bacillus stearothermophilus α-amylase (BStA) preferentially hydrolysed the exterior chains of amylopectin. However, during the later phases, BStA also hydrolysed inner chains, presumably with a high multiple Attack Action. The present results clearly show that different enzymes can be used for (limited) conversion of amylopectin into structures differing in molecular weight and chain length distributions.
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Amylase Action pattern on starch polymers
Biologia, 2008Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:Several decades ago, the first reports on differences in Action pattern between amylases from different sources indicated that the starch polymers are not degraded in a completely random manner. We here give an overview of different Action patterns of amylases on amylose and amylopectin, focusing on the so-called multiple Attack Action of the enzymes. Nowadays, the multiple Attack Action is generally an accepted concept to explain the differences in amylase Action pattern. However, the pancreatic α -amylase remains one of the few enzymes known with a considerable level of multiple Attack Action. Despite some recent studies, the molecular mechanism of the multiple Attack Action is still largely unclear. Probably, the degree to which the active site architecture and binding properties allow both the reorganization (sliding) of the substrate in the active site and the stabilisation of the productive enzyme/substrate complex mainly determine the multiple Attack Action of amylases.
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Temperature impacts the multiple Attack Action of amylases
Biomacromolecules, 2007Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:The Action pattern of several amylases was studied at 35, 50, and 70 °C using potato amylose, a soluble (Red Starch) and insoluble (cross-linked amylose) chromophoric substrate. With potato amylose as substrate, Bacillus stearothermophilus α-amylase (BStA) and porcine pancreatic α-amylase displayed a high degree of multiple Attack (DMA, i.e., the number of bonds broken during the lifetime of an enzyme−substrate complex minus one), the fungal α-amylase from Aspergillus oryzae a low DMA, and the α-amylases from B. licheniformis, Thermoactinomyces vulgaris, B. amyloliquifaciens, and B. subtilis an intermediate DMA. These data are discussed in relation to structural properties of the enzymes. The level of multiple Attack (LMA), based on the relation between the drop in iodine binding of amylose and the increase in total reducing value, proved to be a good alternative for DMA measurements. The LMA of the endo-amylases increased with temperature to a degree depending on the amylase. In contrast, BStA showed a d...
Annabel Bijttebier - One of the best experts on this subject based on the ideXlab platform.
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Hydrolysis of amylopectin by amylolytic enzymes: structural analysis of the residual amylopectin population.
Carbohydrate Research, 2009Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:Abstract Amylopectin fine structures were studied following limited hydrolysis of gelatinised waxy maize starch by amylases with a different level of inner chain Attack (LICA). This was done by size exclusion chromatography as well as by debranching the (partially hydrolysed) amylopectin samples and studying the size distributions of the released chains. α-Amylases from Bacillus amyloliquefaciens and Aspergillus oryzae , with a relatively high LICA, drastically altered amylopectin chain length distribution and reduced the amylopectin molecular size (MS) significantly even at a low to moderate degree of hydrolysis (DH). Porcine pancreatic α-amylase (PPA), with a rather low LICA but a high multiple Attack Action on amylose, reduced the amylopectin MS much slower. Following hydrolysis by PPA to a DH of 10% and enzymic debranching of the amylopectin residue, several subpopulations of chains consisting of 2–12 glucose units were detected, indicating a multiple Attack Action on the amylopectin side chains. During the early stages of hydrolysis, the maltogenic Bacillus stearothermophilus α-amylase (BStA) preferentially hydrolysed the exterior chains of amylopectin. However, during the later phases, BStA also hydrolysed inner chains, presumably with a high multiple Attack Action. The present results clearly show that different enzymes can be used for (limited) conversion of amylopectin into structures differing in molecular weight and chain length distributions.
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Amylase Action pattern on starch polymers
Biologia, 2008Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:Several decades ago, the first reports on differences in Action pattern between amylases from different sources indicated that the starch polymers are not degraded in a completely random manner. We here give an overview of different Action patterns of amylases on amylose and amylopectin, focusing on the so-called multiple Attack Action of the enzymes. Nowadays, the multiple Attack Action is generally an accepted concept to explain the differences in amylase Action pattern. However, the pancreatic α -amylase remains one of the few enzymes known with a considerable level of multiple Attack Action. Despite some recent studies, the molecular mechanism of the multiple Attack Action is still largely unclear. Probably, the degree to which the active site architecture and binding properties allow both the reorganization (sliding) of the substrate in the active site and the stabilisation of the productive enzyme/substrate complex mainly determine the multiple Attack Action of amylases.
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Temperature impacts the multiple Attack Action of amylases
Biomacromolecules, 2007Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:The Action pattern of several amylases was studied at 35, 50, and 70 °C using potato amylose, a soluble (Red Starch) and insoluble (cross-linked amylose) chromophoric substrate. With potato amylose as substrate, Bacillus stearothermophilus α-amylase (BStA) and porcine pancreatic α-amylase displayed a high degree of multiple Attack (DMA, i.e., the number of bonds broken during the lifetime of an enzyme−substrate complex minus one), the fungal α-amylase from Aspergillus oryzae a low DMA, and the α-amylases from B. licheniformis, Thermoactinomyces vulgaris, B. amyloliquifaciens, and B. subtilis an intermediate DMA. These data are discussed in relation to structural properties of the enzymes. The level of multiple Attack (LMA), based on the relation between the drop in iodine binding of amylose and the increase in total reducing value, proved to be a good alternative for DMA measurements. The LMA of the endo-amylases increased with temperature to a degree depending on the amylase. In contrast, BStA showed a d...
Hans Goesaert - One of the best experts on this subject based on the ideXlab platform.
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Hydrolysis of amylopectin by amylolytic enzymes: structural analysis of the residual amylopectin population.
Carbohydrate Research, 2009Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:Abstract Amylopectin fine structures were studied following limited hydrolysis of gelatinised waxy maize starch by amylases with a different level of inner chain Attack (LICA). This was done by size exclusion chromatography as well as by debranching the (partially hydrolysed) amylopectin samples and studying the size distributions of the released chains. α-Amylases from Bacillus amyloliquefaciens and Aspergillus oryzae , with a relatively high LICA, drastically altered amylopectin chain length distribution and reduced the amylopectin molecular size (MS) significantly even at a low to moderate degree of hydrolysis (DH). Porcine pancreatic α-amylase (PPA), with a rather low LICA but a high multiple Attack Action on amylose, reduced the amylopectin MS much slower. Following hydrolysis by PPA to a DH of 10% and enzymic debranching of the amylopectin residue, several subpopulations of chains consisting of 2–12 glucose units were detected, indicating a multiple Attack Action on the amylopectin side chains. During the early stages of hydrolysis, the maltogenic Bacillus stearothermophilus α-amylase (BStA) preferentially hydrolysed the exterior chains of amylopectin. However, during the later phases, BStA also hydrolysed inner chains, presumably with a high multiple Attack Action. The present results clearly show that different enzymes can be used for (limited) conversion of amylopectin into structures differing in molecular weight and chain length distributions.
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Amylase Action pattern on starch polymers
Biologia, 2008Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:Several decades ago, the first reports on differences in Action pattern between amylases from different sources indicated that the starch polymers are not degraded in a completely random manner. We here give an overview of different Action patterns of amylases on amylose and amylopectin, focusing on the so-called multiple Attack Action of the enzymes. Nowadays, the multiple Attack Action is generally an accepted concept to explain the differences in amylase Action pattern. However, the pancreatic α -amylase remains one of the few enzymes known with a considerable level of multiple Attack Action. Despite some recent studies, the molecular mechanism of the multiple Attack Action is still largely unclear. Probably, the degree to which the active site architecture and binding properties allow both the reorganization (sliding) of the substrate in the active site and the stabilisation of the productive enzyme/substrate complex mainly determine the multiple Attack Action of amylases.
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Temperature impacts the multiple Attack Action of amylases
Biomacromolecules, 2007Co-Authors: Annabel Bijttebier, Hans Goesaert, Jan A. DelcourAbstract:The Action pattern of several amylases was studied at 35, 50, and 70 °C using potato amylose, a soluble (Red Starch) and insoluble (cross-linked amylose) chromophoric substrate. With potato amylose as substrate, Bacillus stearothermophilus α-amylase (BStA) and porcine pancreatic α-amylase displayed a high degree of multiple Attack (DMA, i.e., the number of bonds broken during the lifetime of an enzyme−substrate complex minus one), the fungal α-amylase from Aspergillus oryzae a low DMA, and the α-amylases from B. licheniformis, Thermoactinomyces vulgaris, B. amyloliquifaciens, and B. subtilis an intermediate DMA. These data are discussed in relation to structural properties of the enzymes. The level of multiple Attack (LMA), based on the relation between the drop in iodine binding of amylose and the increase in total reducing value, proved to be a good alternative for DMA measurements. The LMA of the endo-amylases increased with temperature to a degree depending on the amylase. In contrast, BStA showed a d...
Chikafusa Fukazawa - One of the best experts on this subject based on the ideXlab platform.
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Kinetic and structural analysis of enzyme sliding on a substrate: multiple Attack in beta-amylase.
Biochemistry, 2007Co-Authors: Kazuhiko Ishikawa, Hiroshi Nakatani, Yoshio Katsuya, Chikafusa FukazawaAbstract:β-Amylase (EC 3.2.1.2) is starch-hydrolyzing exo-type enzyme that can catalyze the successive liberation of β-maltose from the nonreducing ends of α-1,4-linked glucopyranosyl polymers. There is a well-known phenomenon called multiple or repetitive Attack where the enzyme releases several maltose molecules in a single enzyme−substrate complex. In order to understand it further, we examined the β-amylase-catalyzed reAction using maltooligosaccharides. The Monte Carlo method was applied for simulation of the β-amylase-catalyzed reAction including the multiple Attack mechanism. Through site-directed mutagenesis, we have successfully prepared a mutant enzyme which may be simulated as a multiple Attack Action reduced one with retaining significant hydrolytic activity. From the results of X-ray structure analysis of the mutant enzyme, it was clarified that one carboxyl residue plays a very important role in the multiple Attack. The multiple Attack Action needs the force of enzyme sliding on the substrate. In add...
Shanchieh Jay Yang - One of the best experts on this subject based on the ideXlab platform.
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Framework to Describe Intentions of a Cyber Attack Action
arXiv: Cryptography and Security, 2020Co-Authors: Stephen Moskal, Shanchieh Jay YangAbstract:The techniques and tactics used by cyber adversaries are becoming more sophisticated, ironically, as defense getting stronger and the cost of a breach continuing to rise. Understanding the thought processes and behaviors of adversaries is extremely challenging as high profile or even amateur Attackers have no incentive to share the trades associated with their illegal activities. One opportunity to observe the Actions the adversaries perform is through the use of Intrusion Detection Systems (IDS) which generate alerts in the event that suspicious behavior was detected. The alerts raised by these systems typically describe the suspicious Actions via the form of Attack 'signature', which do not necessarily reveal the true intent of the Attacker performing the Action. Meanwhile, several high level frameworks exist to describe the sequence or chain of Action types an adversary might perform. These frameworks, however, do not connect the Action types to observables of standard intrusion detection systems, nor describing the plausible intents of the adversarial Actions. To address these gaps, this work proposes the Action-Intent Framework (AIF) to complement existing Cyber Attack Kill Chains and Attack Taxonomies. The AIF defines a set of Action-Intent States (AIS) at two levels of description: the Macro-AIS describes 'what' the Attacker is trying to achieve and the Micro-AIS describes "how" the intended goal is achieved. A full description of both the Macro is provided along with a set of guiding principals of how the AIS is derived and added to the framework.
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sequential modeling for obfuscated network Attack Action sequences
Communications and Networking Symposium, 2013Co-Authors: Shanchieh Jay YangAbstract:This work presents a preliminary study of modeling obfuscation techniques for network Attack Action sequences. The aim is to develop a systematic analytical methodology that shows how intentional obfuscation or unintentional noise may affect the modeling and classification of Attack sequences. Discussions on different types of obfuscation techniques will be given, followed by a formal formulation to represent the effect of obfuscation within Attack sequences. Preliminary simulation results are presented to demonstrate the impact of Attack sequences with and without obfuscated Attack Actions.
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CNS - Sequential modeling for obfuscated network Attack Action sequences
2013 IEEE Conference on Communications and Network Security (CNS), 2013Co-Authors: Shanchieh Jay YangAbstract:This work presents a preliminary study of modeling obfuscation techniques for network Attack Action sequences. The aim is to develop a systematic analytical methodology that shows how intentional obfuscation or unintentional noise may affect the modeling and classification of Attack sequences. Discussions on different types of obfuscation techniques will be given, followed by a formal formulation to represent the effect of obfuscation within Attack sequences. Preliminary simulation results are presented to demonstrate the impact of Attack sequences with and without obfuscated Attack Actions.
