Luminal starch substrate brake on maltase-glucoamylase activity is located within the glucoamylase subunit
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type: Document
type: Continuant
estado: published
type: Article
chemicalscas: acarbose, 56180-94-0; alpha glucosidase, 9001-42-7; glucan, 9012-72-0, 9037-91-6; glucan 1,4 alpha glucosidase, 9032-08-0; glucose, 50-99-7, 84778-64-3; maltodextrin, 9050-36-6; maltose, 16984-36-4, 69-79-4; starch, 9005-25-8, 9005-84-9
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issue: 4
pmid: 18356321
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abstract: The detailed mechanistic aspects for the final starch digestion process leading to effective α-glucogenesis by the 2 mucosal α-glucosidases, human sucrase-isomaltase complex (SI) and human maltase-glucoamylase (MGAM), are poorly understood. This is due to the structural complexity and vast variety of starches and their intermediate digestion products, the poorly understood enzyme-substrate interactions occurring during the digestive process, and the limited knowledge of the structure-function properties of SI and MGAM. Here we analyzed the basic catalytic properties of the N-terminal subunit of MGAM (ntMGAM) on the hydrolysis of glucan substrates and compared it with those of human native MGAM isolated by immunochemical methods. In relation to native MGAM, ntMGAM displayed slower activity against maltose to maltopentose (G5) series glucose oligomers, as well as maltodextrins and α-limit dextrins, and failed to show the strong substrate inhibitory brake effect caused by maltotriose, maltotetrose, and G5 on the native enzyme. In addition, the inhibitory constant for acarbose was 2 orders of magnitude higher for ntMGAM than for native MGAM, suggesting lower affinity and/or fewer binding configurations of the active site in the recombinant enzyme. The results strongly suggested that the C-terminal subunit of MGAM has a greater catalytic efficiency due to a higher affinity for glucan substrates and larger number of binding configurations to its active site. Our results show for the first time, to our knowledge, that the C-terminal subunit of MGAM is responsible for the MGAM peptide%27s glucoamylase activity and is the location of the substrate inhibitory brake. In contrast, the membrane-bound ntMGAM subunit contains the poorly inhibitable maltase activity of the internally duplicated enzyme. © 2008 American Society for Nutrition.
most specific type: Article
type: Generically Dependent Continuant
doi: 10.1093/jn/138.4.685
has publication venue: Journal of Nutrition
crisid: 1925
page start: 685
volume: 138
related by: authorship_11453
accesstype: All Open Access, Bronze
page end: 692
freetext keyword: acarbose; alpha glucosidase; glucan; glucan 1,4 alpha glucosidase; glucose; maltodextrin; maltopentose; maltose; oligomer; starch; sucrase isomaltase; unclassified drug; amino terminal sequence; article; carbohydrate metabolism; carboxy terminal sequence; catalysis; enzyme active site; enzyme activity; enzyme binding; enzyme inhibition; enzyme mechanism; enzyme substrate complex; glucogenesis; human; hydrolysis; immunochemistry; mucosa; protein function; structure activity relation
related by: authorship_11449
e iscopus: 2-s2.0-41549159900
abstract: The detailed mechanistic aspects for the final starch digestion process leading to effective α-glucogenesis by the 2 mucosal α-glucosidases, human sucrase-isomaltase complex (SI) and human maltase-glucoamylase (MGAM), are poorly understood. This is due to the structural complexity and vast variety of starches and their intermediate digestion products, the poorly understood enzyme-substrate interactions occurring during the digestive process, and the limited knowledge of the structure-function properties of SI and MGAM. Here we analyzed the basic catalytic properties of the N-terminal subunit of MGAM (ntMGAM) on the hydrolysis of glucan substrates and compared it with those of human native MGAM isolated by immunochemical methods. In relation to native MGAM, ntMGAM displayed slower activity against maltose to maltopentose (G5) series glucose oligomers, as well as maltodextrins and α-limit dextrins, and failed to show the strong substrate inhibitory brake effect caused by maltotriose, maltotetrose, and G5 on the native enzyme. In addition, the inhibitory constant for acarbose was 2 orders of magnitude higher for ntMGAM than for native MGAM, suggesting lower affinity and/or fewer binding configurations of the active site in the recombinant enzyme. The results strongly suggested that the C-terminal subunit of MGAM has a greater catalytic efficiency due to a higher affinity for glucan substrates and larger number of binding configurations to its active site. Our results show for the first time, to our knowledge, that the C-terminal subunit of MGAM is responsible for the MGAM peptide's glucoamylase activity and is the location of the substrate inhibitory brake. In contrast, the membrane-bound ntMGAM subunit contains the poorly inhibitable maltase activity of the internally duplicated enzyme. © 2008 American Society for Nutrition.
date time value: article date 1925
related by: authorship_11451
related by: authorship_11454
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