Brain glucose-6-phosphatase

Another class of carbohydrate and fatty acid metabolism disorders is caused by systemic metabolic defects that affect the brain. Glucose-6-phosphatase deficiency (glycogenosis type I, Von Gierke s disease)... 

Glucose-6-phosphatase is found only in liver and kidney, and allows these tissues to supply glucose to other organs of the body, like the brain, which have little or no reserves of carbohydrates. 

Another indication of the difference between the metabolic roles of muscle, a consumer tissue and liver, a contributer tissue, is the enzyme glucose-6-phospha-tase. This enzyme is required for the production of neutral glucose. It is present in liver and kidney but not in strict consumer tissues, such as muscle and brain. Without glu-cose-6-phosphatase the glucose-6-phosphate cannot be converted to dephosphorylated glucose, which is necessary for... 

The main site of gluconeogenesis is the liver, although it also occurs to a far lesser extent in the kidneys. Very little gluconeogenesis occurs in brain or muscle. Within liver cells, the first enzyme of gluconeogenesis, pyruvate carboxylase, is located in the mitochondrial matrix. The last enzyme, glucose 6-phosphatase is bound to the smooth endoplasmic reticulum. The other enzymes of the pathway are located in the cytosol. 

The liver and to a lesser extent the kidneys, contain glucose 6-phosphatase, whereas muscle and the brain do not. Hence, muscle and the brain, in contrast with the liver, do not release glucose. Another key enzymatic difference is that the liver has little of the transferase needed to activate acetoacetate to acetoacetyl CoA. Consequently, acetoacetate and 3-hydroxybutyrate are exported by the liver for use by heart muscle, skeletal muscle, and the brain. 

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