What's so important about glucose 6-phosphate anyway?

When your cells are in a low-energy state, they are hungry.

• Free glucose is converted to glucose 6-phosphate (G6P) by hexokinase/glucokinase (1). The reaction requires an investment of 1 ATP molecule, but effectively traps glucose within the cell (1).
• Glycogen is broken down to G1P and subsequently G6P (2p80-81). The G6P can then be used in metabolic pathways or, in the liver and kidneys, be converted back to glucose (2p80-81).
• In a hypoglycemic state, G6P can also formed from gluconeogenesis from non-carbohydrate sources (2p98).

G6P can then enter glycolysis to produce ATP or, if biosynthesis is needed, the hexomonophosphate shunt to produce NADP for fatty acid synthesis (2p84;95).

In a high-energy state (when cells are not hungry), G6P plays a role in the following.

• G6P negatively modulates the hexokinase/glucokinase reaction (2p84).
• G6P enters glycogenesis producing glycogen for storage of glucose (2p99). Glucose is now believed to enter glycogenesis via gluconeogenesis, first converting to lactate, taken up by the liver and converted to G6P (2p99).

Reference List

1.Dennison KJ, Topping J, Caret RL. General, Organic, and Biochemistry. New York: McGraw-Hill, 2007.
2.Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.

Note: Here's a neat animation: http://www.science.smith.edu/departments/Biology/Bio231/