fosfoglucosa

Fosfoglucosa, or glucosa-6-fosfato (G6P), is the phosphorylated form of glucose in which a phosphate group is esterified to the sixth carbon. It is a central metabolite in carbohydrate metabolism with the chemical formula C6H13O9P and carries a negative charge at physiological pH.

Biosynthesis and metabolic role: G6P is produced in the cytosol by the phosphorylation of glucose through the action of hexokinase or glucokinase, using ATP. It serves as a key junction in metabolism: it can be isomerized to fructosa-6-phosphate by phosphoglucose isomerase to continue glycolysis, or it can enter the oxidative or non-oxidative branches of the pentose phosphate pathway via glucose-6-phosphate dehydrogenase to generate NADPH and ribose-5-phosphate. G6P is also a precursor for glycogen synthesis through conversion to glucose-1-phosphate and UDP-glucose.

Cellular localization and glucose homeostasis: In most cells, G6P remains in the cytosol. In liver and kidney cells, glucose-6-phosphatase located in the endoplasmic reticulum dephosphorylates G6P to glucose, enabling glucose release into the bloodstream during gluconeogenesis or fasting. This reaction requires the glucose-6-phosphate transporter to move G6P into the ER lumen.

Physiological and clinical significance: As a metabolic crossroads, G6P integrates glycolysis, gluconeogenesis, and the pentose phosphate pathway, influencing energy balance and reductive power. Defects in related enzymes or transporters (for example, glucose-6-phosphatase or G6P transporters) can cause glycogen storage diseases, such as von Gierke disease, or related metabolic disorders affecting glucose homeostasis.