In enzymology, an alternansucrase is an enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that catalyzes

Catalysis

Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....

 a chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

 that transfers an alpha-D-glucosyl residue

Glucose

Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 from sucrose

Sucrose

Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...

 alternately to the 6- and 3-positions of the non-reducing terminal residue of an alpha-D-glucan

Glucan

A glucan molecule is a polysaccharide of D-glucose monomers linked by glycosidic bonds.Many beta-glucans are medically important.-Types:The following are glucans:-Alpha:...

, thereby creating a glucan with alternating alpha-1,6- and alpha-1,3-bonds. The name "alternan" was coined in 1982 (Cote & Robyt) for the glucan based on its alternating linkage structure.

This enzyme belongs to the family of glycosyltransferase

Glycosyltransferase

Glycosyltransferases are enzymes that act as a catalyst for the transfer of a monosaccharide unit from an activated nucleotide sugar to a glycosyl acceptor molecule, usually an alcohol....

s, specifically the hexosyltransferases. The systematic name of this enzyme class is sucrose:1,6(1,3)-alpha-D-glucan 6(3)-alpha-D-glucosyltransferase. Other names in common use include sucrose-1,6(3)-alpha-glucan 6(3)-alpha-glucosyltransferase, sucrose:1,6-, 1,3-alpha-D-glucan 3-alpha- and, and 6-alpha-D-glucosyltransferase.