In enzymology, a xylose isomerase (EC 5.3.1.5) is an enzyme that catalyzes the interconversion ofD-xylose and D-xylulose. This enzyme belongs to the family of isomerases, specifically those intramolecular oxidoreductases interconverting aldoses and ketoses. The isomerase has now been observed in nearly a hundred species of bacteria. Xylose-isomerases are also commonly called glucose isomerase or fructose isomerases due to their ability to interconvert glucose and fructose. The systematic name of this enzyme class is α-D-xylopyranose aldose-ketose-isomerase. Other names in common use include D-xylose isomerase, D-xylose ketoisomerase, and D-xylose ketol-isomerase.