In
enzymology
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
, a starch synthase () is an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
that
catalyzes the
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
:ADP-glucose + (1,4-alpha-D-glucosyl)
n ADP + (1,4-alpha-D-glucosyl)
n+1
Thus, the two
substrates of this enzyme are
ADP-glucose and a chain of D-
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
residues joined by 1,4-alpha-
glycosidic bond
A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
A glycosidic bond is formed between the hemiacetal or hemiketal group ...
s, whereas its two
products
Product may refer to:
Business
* Product (business), an item that serves as a solution to a specific consumer problem.
* Product (project management), a deliverable or set of deliverables that contribute to a business solution
Mathematics
* Produ ...
are
ADP and an elongated chain of glucose residues.
Plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s use these enzymes in the biosynthesis of
starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...
.
This enzyme belongs to the family of
hexosyltransferase Hexosyltransferases are a type of glycosyltransferase that catalyze the transfer of a hexose.
Examples include:
* glucosyltransferases - transfer glucose
* galactosyltransferases - transfer galactose
* fucosyltransferases - transfer fucose
* ...
s, specifically the
glycosyltransferase
Glycosyltransferases (GTFs, Gtfs) are enzymes ( EC 2.4) that establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar (also known as the "glycosyl donor") to a nucleophilic glycos ...
s. The
systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature.
A semisystematic name or semitrivial ...
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
A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
have been solved for this class of enzymes, with
PDB accession codes , , , and .
References
*
*
*
*
* Whelan, W.J. and Schultz, J. (Eds.), Miami Winter Symposia, vol. 1, North Holland, Utrecht, 1970, p. 122-138.
EC 2.4.1
Enzymes of known structure
Starch
{{2.4-enzyme-stub