Glucose-6-phosphatase glycogen, conversion

Conversion of the D form back to the I form requires action of the enzyme phosphoprotein phosphatase I. Glycogen synthase I is called the independent form of glycogen synthase, since it does not require glucose-6-phosphate for activity. 

In the previous section we considered three possible pathways for glucose-6-phosphate dephosphorylation by glucose-6-phosphatase, conversion to fructose-6-phosphate followed by oxidation through the Embden-Meyerhof pathway, and conversion to glucose-1-phosphate followed by glycogen synthesis. A fourth pathway exists—the hexose monophosphate shunt [61-63]. 

Epinephrine is a hormone that causes extremely rapid responses. One of the responses to this hormone is an increased liberation of liver glycogen as glucose. This reaction has been found to be limited by the enzyme phosphorylase. Liver phosphorylase exists as the active enzyme and as the inactive, dephosphophosphorylase. Epinephrine, and also the hyperglycemic factor, glucagon, have been found to stimulate the formation of active phosphorylase. This stimulation is mediated by an adenine nucleotide liberated from cell particles by an action of the hormones. The liberation of the nucleotide has been demonstrated in cell-free systems. The nucleotide in an unexplained manner, perhaps indirectly or after metabolic conversion to another form, alters the activity of either the kinase or the phosphatase so that the steady-state concentration of active phosphorylase is increased, i ... 

A galactose or fructose tolerance test normally results in a rise in blood sugar levels as a result of their conversion in the liver by a series of enzymes including glucose-6-phosphatase. In Type I glycogen storage disease this does not occur. 

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