Phosphate sugar isomerases and their potential for rare sugar bioconversion

Phosphate sugar isomerases, catalyzing the isomerization between ketopentose/ketohexose phosphate and aldopentose/aldohexose phosphate, play an important role in microbial sugar metabolism. They are present in a wide range of microorganisms. They have attracted increasing research interest because of their broad substrate specificity and great potential in the enzymatic production of various rare sugars. Here, the enzymatic properties of various phosphate sugar isomerases are reviewed in terms of their substrate specificities and their applications in the production of valuable rare sugars because of their functions such as low-calorie sweeteners, bulking agents, and pharmaceutical precursor. Specifically, we focused on the industrial applications of D -ribose-5-phosphate isomerase and D -mannose-6-phosphate isomerase to produce D -allose and L -ribose, respectively.