Starch synthase

In enzymology, a starch synthase (EC 2.4.1.21) is an enzyme that catalyzes the chemical reaction

ADP-glucose + (1,4-alpha-D-glucosyl)n ADP + (1,4-alpha-D-glucosyl)n+1
starch synthase
Identifiers
EC number2.4.1.21
CAS number9030-10-8
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO

Thus, the two substrates of this enzyme are ADP-glucose and a chain of D-glucose residues joined by 1,4-alpha-glycosidic bonds, whereas its two products are ADP and an elongated chain of glucose residues. Plants use these enzymes in the biosynthesis of starch.

This enzyme belongs to the family of hexosyltransferases, specifically the glycosyltransferases. The systematic name of this enzyme class is ADP-glucose:1,4-alpha-D-glucan 4-alpha-D-glucosyltransferase. Other names in common use include ADP-glucose-starch glucosyltransferase, adenosine diphosphate glucose-starch glucosyltransferase, adenosine diphosphoglucose-starch glucosyltransferase, ADP-glucose starch synthase, ADP-glucose synthase, ADP-glucose transglucosylase, ADP-glucose-starch glucosyltransferase, ADPG starch synthetase, and ADPG-starch glucosyltransferase

Five isoforms seems to be present. GBSS which is linked to amylose synthesis. The others are SS1, SS2, SS3 and SS4. These have different roles in amylopectin synthesis. New work implies that SS4 is important for granule initiation. (Szydlowski et al., 2011)

Structural studies

As of late 2007, 4 structures have been solved for this class of enzymes, with PDB accession codes 1RZU, 1RZV, 2BFW, and 2BIS.

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References
    • Chambers J, Elbein AD (1970). "Biosynthesis of glucans in mung bean seedlings. Formation of beta-(1,4)-glucans from GDP-glucose and beta-(1,3)-glucans from UDP-glucose". Arch. Biochem. Biophys. 138 (2): 620–31. doi:10.1016/0003-9861(70)90389-9. PMID 4317490.
    • FRYDMAN RB, CARDINI CE (1965). "STUDIES ON ADENOSINE DIPHOSPHATE D-GLUCOSE: ALPHA-1,4-GLUCAN ALPHA-4-GLUCOSYLTRANSFERASE OF SWEET-CORN ENDOSPERM". Biochim. Biophys. Acta. 96: 294–303. doi:10.1016/0926-6593(65)90013-5. PMID 14298833.
    • Greenberg E; Preiss J (1965). "Biosynthesis of bacterial glycogen. II. Purification and properties of the adenosine diphosphoglucose:glycogen transglucosylase of arthrobacter species NRRL B1973". J. Biol. Chem. 240: 2341–2348. PMID 14304835.
    • Leloir LF, de Fekete MA, Cardini CE (1961). "Starch and oligosaccharide synthesis from uridine diphosphate glucose". J. Biol. Chem. 236: 636–641. PMID 13760681.
    • Whelan, W.J. and Schultz, J. (Eds.), Miami Winter Symposia, vol. 1, North Holland, Utrecht, 1970, p. 122-138.


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