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1,4-alpha-glucan branching enzyme
Identifiers
Symbol	GBE1
Entrez	2632
HUGO	4180
OMIM	607839
RefSeq	NM_000158
UniProt	Q04446
Other data
EC number	2.4.1.18
Locus	Chr. 3 p12

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 catalyzed by the enzyme glycogen synthase.

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 transferases, specifically those glycosyltransferases that transfer hexoses (hexosyltransferases). 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.

Contents 1 Pathology 2 Structural studies 3 References 4 External links 4.1 Gene Ontology (GO) codes

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 structure has been solved for this class of enzymes, with the PDB accession code 1M7X.

References

• IUBMB entry for 2.4.1.18
• BRENDA references for 2.4.1.18 (Recommended.)
• PubMed references for 2.4.1.18
• PubMed Central references for 2.4.1.18
• Google Scholar references for 2.4.1.18
• Barker SA, Bourne E and Peat S (Lond.). "The enzymic synthesis and degradation of starch. Part IV. The purification and storage of the Q-enzyme of the potato". J. Chem. Soc.: 1705–1711. 
• Baum H and Gilbert GA (1953). "A simple method for the preparation of crystalline potato phosphorylase and Q-enzyme". Nature 171: 983–984. doi:10.1038/171983a0. 
• Hehre EJ (1951). "Enzymic synthesis of polysaccharides: a biological type of polymerization". Adv. Enzymol. Relat. Subj. Biochem. 11: 297–337. doi:10.1002/9780470122563.ch6. 
• Handelsman DJ (2006). "Follicle-stimulating hormone increases primordial follicle reserve in mature female hypogonadal mice". J. Endocrinol. 188: 549–57. doi:10.1677/joe.1.06614. PMID 16522734. 

External links

The CAS registry number for this enzyme class is 9001-97-2.

• IUBMB entry for 2.4.1.18

• KEGG entry for 2.4.1.18

• BRENDA entry for 2.4.1.18

• NiceZyme view of 2.4.1.18

• EC2PDB: PDB structures for 2.4.1.18

• PRIAM entry for 2.4.1.18

• PUMA2 entry for 2.4.1.18

• IntEnz: Integrated Enzyme entry for 2.4.1.18

• MetaCyc entry for 2.4.1.18

• Atomic-resolution structures of enzymes belonging to this class

Gene Ontology (GO) codes

• EGO entry for GO code 0003844: glycogen branching enzyme

• AMIGO entry for GO code 0003844: glycogen branching enzyme

v • d • e Transferases: glycosyltransferases (EC 2.4) 2.4.1 - Hexosyltransferases Glucosyltransferase Phosphorylase (Starch, Glycogen, Myo-) - Glycogen synthase - Debranching enzyme - Branching enzyme - 1,3-beta-glucan synthase - Ceramide glucosyltransferase Galactosyltransferase Lactose synthase - B-N-acetylglucosaminyl-glycopeptide b-1,4-galactosyltransferase Glucuronosyltransferase UGT1A1 - UGT2B7 - Hyaluronan synthase Fucosyltransferase POFUT1 - POFUT2 2.4.2 - Pentosyltransferases ADP ribose Cholera toxin - Diphtheria toxin - Pertussis toxin - Poly ADP ribose polymerase Other Purine nucleoside phosphorylase - Adenine phosphoribosyltransferase - Hypoxanthine-guanine phosphoribosyltransferase - Uracil phosphoribosyltransferase - Amidophosphoribosyltransferase - Xylosyltransferase

v • d • e Metabolism: carbohydrate metabolism - glycogenesis and glycogenolysis enzymes Glycogenesis Phosphoglucomutase - UDP-glucose pyrophosphorylase - Glycogen synthase (Glycogen branching enzyme) Glycogenolysis Glycogen phosphorylase (Debranching enzyme) - Phosphoglucomutase - Glycogenin Maltase Regulation Phosphorylase kinase - Phosphoprotein phosphatase

Wikipedia content modification information:

• This page was last modified on 28 May 2008, at 14:39.

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