Starch Branching Enzyme Information

A glycogen branching enzyme is an enzyme that takes part in converting glucose to glycogen. It adds branches to the growing 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, to be specific, 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.

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

• 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 (4361): 983–984. doi:10.1038/171983a0. PMID 13063502.
• Hehre EJ (1951). Enzymic Synthesis of Polysaccharides: a Biological type of Polymerization. "Advances in Enzymology and Related Areas of Molecular Biology". Adv. Enzymol. Relat. Subj. Biochem.. Advances in Enzymology - and Related Areas of Molecular Biology 11: 297–337. doi:10.1002/9780470122563.ch6. ISBN 9780470122563.
• Handelsman DJ; Wang, Y; Jimenez, M; Marshan, B; Spaliviero, J; Illingworth, P; Handelsman, DJ (2006). "Follicle-stimulating hormone increases primordial follicle reserve in mature female hypogonadal mice". J. Endocrinol. 188 (3): 549–57. doi:10.1677/joe.1.06614. PMID 16522734.

External links

• GeneReviews/NCBI/NIH/UW entry on Adult Polyglucosan Body Disease
• OMIM entries on Adult Polyglucosan Body Disease

Categories: Genes on chromosome 3 | EC 2.4.1 | Enzymes of known structure | Enzymes | Metabolism | Transferases |

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See Also:

• Branches
• Enzyme
• Enzyme Inhibitor
• Enzyme Inhibitors
• Hydroxyethylstarch
• Hydroxypropyl Distarch Phosphate
• Resistant Starch
• Starch
• Starchtapioca Starch Arrowroot Starch Mung Bean Starch