Glycogen branching enzyme
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215507415
2008-05-28T14:39:16Z
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{{protein
|Name=1,4-alpha-glucan branching enzyme
|caption=
|image=
|width=
|HGNCid=4180
|Symbol=GBE1
|AltSymbols=
|EntrezGene=2632
|OMIM=607839
|RefSeq=NM_000158
|UniProt=Q04446
|PDB=
|ECnumber=2.4.1.18
|Chromosome=3
|Arm=p
|Band=12
|LocusSupplementaryData=
}}
A '''glycogen branching enzyme''' is an [[enzyme]] taking part in the [[synthesis]] of [[glycogen]] by adding branches to the glycogen molecule. Glycogen is a branching [[polymer]] of large numbers of [[glucose]] units linked together. The structure is based on chains of glucose units with linkages between [[carbon]] atoms 1 and 4 of each pair of units (alpha 1, 4 linkages). These linkages are [[Catalysis|catalyzed]] by the enzyme [[glycogen synthase]].
[[Image:Glycogen.png|thumb|center|450px|Glycogen structure]]
Every 10 to 14 [[glucose]] units a side branch with an additional chain of glucose units occurs. The [[side chain]] attaches at carbon atom 6 of a glucose unit, and the linkage is termed an alpha-1,6 [[glycosidic]] bond. To form this connection a separate enzyme known as a branching enzyme is used. A branching enzyme attaches a string of seven glucose units to the sixth carbon of a glucose unit, usually in an interior location of the glycogen molecule.
This enzyme belongs to the family of [[transferase]]s, specifically those glycosyltransferases that transfer [[hexose]]s ([[hexosyltransferase]]s). The systematic name of this enzyme class is '''1,4-alpha-D-glucan:1,4-alpha-D-glucan 6-alpha-D-(1,4-alpha-D-glucano)-transferase'''. Other names in common use include '''branching enzyme''', '''amylo-(1,4→1,6)-transglycosylase''', '''Q-enzyme''', '''alpha-glucan-branching glycosyltransferase''', '''amylose isomerase''', '''enzymatic branching factor''', '''branching glycosyltransferase''', '''enzyme Q''', '''glucosan transglycosylase''', '''1,4-alpha-glucan branching enzyme''', '''plant branching enzyme''', '''alpha-1,4-glucan:alpha-1,4-glucan-6-glycosyltransferase''', and '''starch branching enzyme'''. This enzyme participates in [[starch]] and [[sucrose]] metabolism.
==Pathology==
A defect in this enzyme can lead to disease; see [[glycogen storage disease type IV]] and [[glycogen branching enzyme deficiency]].
==Structural studies==
As of late 2007, only one [[tertiary structure|structure]] has been solved for this class of enzymes, with the [[Protein Data Bank|PDB]] accession code {{PDB link|1M7X}}.
==References==
{{reflist|1}}
{{Enzyme references|EC_number=2.4.1.18|IUBMB_EC_number=2/4/1/18}}
* {{cite journal | author = Barker SA, Bourne E and Peat S | date = Lond. | title = The enzymic synthesis and degradation of starch. Part IV. The purification and storage of the Q-enzyme of the potato | journal = J. Chem. | volume = Soc. | pages = 1705–1711 }}
* {{cite journal | author = Baum H and Gilbert GA | date = 1953 | title = A simple method for the preparation of crystalline potato phosphorylase and Q-enzyme | journal = Nature | volume = 171 | pages = 983–984 | doi = 10.1038/171983a0 }}
* {{cite journal | author = Hehre EJ | date = 1951 | title = Enzymic synthesis of polysaccharides: a biological type of polymerization | journal = Adv. Enzymol. Relat. Subj. Biochem. | volume = 11 | pages = 297–337 | doi = 10.1002/9780470122563.ch6 }}
* {{cite journal | author = Handelsman DJ | date = 2006 | title = Follicle-stimulating hormone increases primordial follicle reserve in mature female hypogonadal mice | journal = J. Endocrinol. | volume = 188 | pages = 549–57 | pmid = 16522734 | doi = 10.1677/joe.1.06614 }}
==External links==
::''The [[CAS registry number]] for this enzyme class is {{CAS registry|9001-97-2}}.''
{{Enzyme links|EC_number=2.4.1.18|IUBMB_EC_number=2/4/1/18}}
===Gene Ontology (GO) codes===
{{GO code links | GO_code=0003844 | name=glycogen branching enzyme}}
{{enzyme-stub}}
[[Category:EC 2.4.1]]
[[Category:Enzymes of known structure]]
[[Category:Enzymes]]
[[Category:Metabolism]]
[[Category:Transferases]]
{{transferase-stub}}
{{Glycosyltransferases}}
{{Glycogenesis and glycogenolysis}}