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=== One enzyme with two catalytic sites ===
In mammals and [[yeast]], a single enzyme performs both debranching functions.<ref name="Nakayama"/> The human glycogen debranching enzyme (gene: AGL) is a monomer with a molecular weight of 175 kDa. It has been shown that the two catalytic actions of AGL can function independently of each other, demonstrating that multiple active sites are present. This idea has been reinforced with inhibitors of the active site, such as polyhydroxyamine, which were found to inhibit glucosidase activity while transferase activity was not measurably changed.<ref name=
Some studies have shown that the C-terminal half of yeast GDE is associated with glucosidase activity, while the N-terminal half is associated with glucosyltransferase activity.<ref name=Nakayama/> In addition to these two [[active site]]s, AGL appears to contain a third active site that allows it to bind to a glycogen polymer.<ref name="Gillard"/> Though the complete structure of the GDE in Eukaryotes is yet to be determined it is thought to bind to six glucose molecules of the chain as well as the branched glucose, thus corresponding to 7 subunits within the active site, as shown in the figure below.<ref name = Yamamoto/>
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<ref name="UniProt P35573">{{cite web | url = http://www.uniprot.org/uniprot/P35573 | title = Glycogen debranching enzyme - Homo sapiens (Human) | authorlink = | date = | format = | work = | publisher = UniProt | pages = | language = | archiveurl = | archivedate = | quote = | accessdate = }}</ref>
<ref name="
<ref name="Gillard">{{cite journal | author = Gillard BK, Nelson TE | title = Amylo-1,6-glucosidase/4-alpha-glucanotransferase: use of reversible substrate model inhibitors to study the binding and active sites of rabbit muscle debranching enzyme | journal = Biochemistry | volume = 16 | issue = 18 | pages = 3978–87 |date=September 1977 | pmid = 269742 | doi = 10.1021/bi00637a007 }}</ref>▼
<ref name="Woo">{{cite journal | author = Woo EJ, Lee S, Cha H, Park JT, Yoon SM, Song HN, Park KH | title = Structural insight into the bifunctional mechanism of the glycogen-debranching enzyme TreX from the archaeon Sulfolobus solfataricus | journal = J. Biol. Chem. | volume = 283 | issue = 42 | pages = 28641–8 |date=October 2008 | pmid = 18703518 | pmc = 2661413 | doi = 10.1074/jbc.M802560200 | url = | issn = }}</ref>
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<ref name="MCCarter">{{cite journal | author = McCarter JD, Withers SG | title = Mechanisms of enzymatic glycoside hydrolysis | journal = Curr. Opin. Struct. Biol. | volume = 4 | issue = 6 | pages = 885–92 |date=December 1994 | pmid = 7712292 | doi = 10.1016/0959-440X(94)90271-2| url = }}</ref>
▲<ref name="Gillard">{{cite journal | author = Gillard BK, Nelson TE | title = Amylo-1,6-glucosidase/4-alpha-glucanotransferase: use of reversible substrate model inhibitors to study the binding and active sites of rabbit muscle debranching enzyme | journal = Biochemistry | volume = 16 | issue = 18 | pages = 3978–87 |date=September 1977 | pmid = 269742 | doi = 10.1021/bi00637a007 }}</ref>
<ref name="Yamamoto">{{cite journal | author = Yamamoto E, Makino Y, Omichi K | title = Active site mapping of amylo-alpha-1,6-glucosidase in porcine liver glycogen debranching enzyme using fluorogenic 6-O-alpha-glucosyl-maltooligosaccharides | journal = J. Biochem. | volume = 141 | issue = 5 | pages = 627–34 |date=May 2007 | pmid = 17317688 | doi = 10.1093/jb/mvm065 }}</ref>
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<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="Shen">{{cite journal | author = Shen J, Bao Y, Liu HM, Lee P, Leonard JV, Chen YT | title = Mutations in exon 3 of the glycogen debranching enzyme gene are associated with glycogen storage disease type III that is differentially expressed in liver and muscle | journal = J. Clin. Invest. | volume = 98 | issue = 2 | pages = 352–7 |date=July 1996 | pmid = 8755644 | pmc = 507437 | doi = 10.1172/JCI118799 }}</ref>
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