Galactose-6-phosphate isomerase  In enzymology, a galactose-6-phosphate isomerase () is an enzyme that catalyzes the chemical reaction  Hence, this enzyme has one substrate, D-galactose 6-phosphate, and one product, D-tagatose 6-phosphate. This enzyme belongs to the family of isomerases, specifically those intramolecular oxidoreductases interconverting aldoses and ketoses. The systematic name of this enzyme class is D-galactose-6-phosphate aldose-ketose-isomerase. This enzyme participates in galactose metabolism.