Phosphohexose

Phosphohexose is a general term used in biochemistry to describe a hexose sugar that has been phosphorylated, carrying a single phosphate group. The phosphate is typically attached to either the first or the sixth carbon of the sugar, yielding derivatives that serve as key intermediates in carbohydrate metabolism. Common examples include glucose-6-phosphate, glucose-1-phosphate, fructose-6-phosphate, and mannose-6-phosphate.

In cells, the addition of a phosphate to a hexose is usually catalyzed by ATP-dependent kinases. Glucose phosphorylation by hexokinase or glucokinase produces glucose-6-phosphate, which feeds into glycolysis and the pentose phosphate pathway. Glucose-6-phosphate can be isomerized to fructose-6-phosphate by phosphohexose isomerase, linking glycolysis with gluconeogenesis. Glucose-1-phosphate enters glycogen synthesis after conversion to UDP-glucose, via phosphoglucomutase and UDP-glucose pyrophosphorylase. Mannose-6-phosphate has roles in lysosomal enzyme targeting in higher organisms.

Phosphohexoses also function as metabolic signals, with their levels influencing flux through glycolysis, the pentose phosphate pathway, and glycogen or lysosomal pathways. Abnormalities in the metabolism or trafficking of sugar phosphates can contribute to metabolic disorders or lysosomal storage diseases.

Terminology-wise, the term phosphohexose refers to any hexose sugar bearing a single phosphate group. An important enzyme in this context is phosphohexose isomerase (glucose-6-phosphate isomerase), which catalyzes the reversible interconversion between glucose-6-phosphate and fructose-6-phosphate.