glucose6phosphate

Glucose-6-phosphate, abbreviated G6P, is the phosphorylated form of glucose in which a phosphate group is attached to carbon 6. It is formed in the cytosol by the transfer of a phosphate from ATP to glucose, a reaction catalyzed by hexokinase or glucokinase. Its molecular formula is C6H13O9P, and it functions as a central metabolic intermediate in many pathways.

G6P is a key branch point in cellular metabolism. In glycolysis, it is isomerized by phosphoglucose isomerase to fructose-6-phosphate, continuing through the glycolytic pathway to generate energy. It also feeds the oxidative phase of the pentose phosphate pathway, where glucose-6-phosphate dehydrogenase converts it to 6-phosphogluconolactone, producing NADPH and ribose-5-phosphate for biosynthesis and antioxidant defenses. In glycogen biosynthesis, G6P can be converted to glucose-1-phosphate by phosphoglucomutase and then to UDP-glucose for incorporation into glycogen.

In gluconeogenesis, G6P is a protected node in the liver (and to a lesser extent the kidney), where glucose-6-phosphatase hydrolyzes it to free glucose that can be released into the bloodstream. This step helps maintain blood glucose during fasting.

Cellular localization and transport are important for G6P’s function. It remains in the cytosol and does not cross membranes readily, so its metabolic fate is governed by the activity and regulation of various enzymes in the same compartment. Regulation of its production and utilization helps coordinate energy production, biosynthesis, and redox balance in cells.