Glycogen debranching enzyme: Difference between revisions

Revision as of 16:57, 2 June 2012

Revision as of 21:00, 4 March 2013

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* 4-α-D-glucanotransferase ({{EC number|2.4.1.25}}), or [[glucosyltransferase]], transfers three glucose [[residue (chemistry)|residues]] from the four-residue glycogen branch to a nearby branch. This exposes a single glucose residue joined to the glucose chain though an α -1,6 glycosidic linkage<ref name="Berg"/>

* Amylo-α-1,6-glucosidase ({{EC number|3.2.1.33}}), or [[glucosidase]], cleaves the remaining alpha-1,6 linkage, producing glucose and a linear chain of glycogen.<ref name=Berg/> The mechanism by which the glucosidase cleaves the α -1,6-linkage is not fully known because the [[amino acids]] in the [[active site]] have not yet been identified. It is thought to proceed through a two step acid base assistance type mechanism, with aan [[oxocarbenium]] ion intermediate, and retention of configuration in glucose.<ref name=Molecule/> This is a common method through which to cleave bonds, with an acid below the site of [[hydrolysis]] to lend a proton and a base above to deprotinate a water which can then act as a [[nucleophile]]. These acids and bases are amino acid side chains in the active site of the enzyme. A scheme for the mechanism is shown in the figure below.<ref name=MCCarter/>

[[File:Glycosidase mechanism.png]]

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== Structure and activity ==

=== Two enzymes ===

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<ref name="Molecule">{{cite journal | author = Chiba S | title = Molecular mechanism in alpha-glucosidase and glucoamylase | journal = Biosci. Biotechnol. Biochem. | volume = 61 | issue = 8 | pages = 1233–9 | year = 1997 | month = August | pmid = 9301101 | doi = | url = }}</ref>

<ref name="Gene">{{cite web | url = http://ghr.nlm.nih.gov/gene/AGL | title = Genes (Genetic Home Reference a service of U.S. National Library of Medicine. | accessdate = February, 29, 2012 }}</ref>

<ref name="Bao">{{cite journal | author = Bao Y, Dawson TL, Chen YT | title = Human glycogen debranching enzyme gene (AGL): complete structural organization and characterization of the 5' flanking region | journal = Genomics | volume = 38 | issue = 2 | pages = 155–65 | year = 1996 | month = December | pmid = 8954797 | doi = 10.1006/geno.1996.0611 }}</ref>