The UDP-forming form of cellulose synthase (EC 2.4.1.12) is the main enzyme that produces cellulose. Systematically, it is known as UDP-glucose:(1→4)-β-D-glucan 4-β-D-glucosyltransferase in enzymology. It catalyzes the chemical reaction:
- UDP-glucose + [(1→4)-β-D-glucosyl]n = UDP + [(1→4)-β-D-glucosyl]n+1
A similar enzyme utilizes GDP-glucose, cellulose synthase (GDP-forming) (EC 2.4.1.29).
This family of enzymes is found in bacteria and plants alike. Plant members are usually known as CesA (cellulose synthase) or the tentative CslA (cellulose synthase-like), while bacterial members may additionally be known as BcsA (bacterial cellulose synthase) or CelA (simply "cellulose"). Plants acquired CesA from the endosymbiosis event that produced the chloroplast. This family belongs to glucosyltransferase family 2 (GT2). Glycosyltransferases are involved in the biosynthesis and hydrolysis of the bulk of earth's biomass. There are known to be about seven subfamilies in the plant CesA superfamily, or ten in the combined plant-algal superfamily. Urochordates are the only group of animals possessing this enzyme, having acquired them by horizontal gene transfer more than 530 million years ago.