Phosphoglucomutase (EC 5.4.2.2) is an enzyme that transfers a phosphate group on an α-D-glucose monomer from the 1' to the 6' position in the forward direction or the 6' to the 1' position in the reverse direction.

More precisely, it facilitates the interconversion of glucose 1-phosphate and glucose 6-phosphate.

After glycogen phosphorylase catalyzes the phosphorolytic cleavage of a glucosyl residue from the glycogen polymer, the freed glucose has a phosphate group on its 1-carbon. This glucose 1-phosphate molecule is not itself a useful metabolic intermediate, but phosphoglucomutase catalyzes the conversion of this glucose 1-phosphate to glucose 6-phosphate (see below for the mechanism of this reaction).

Glucose 6-phosphate’s metabolic fate depends on the needs of the cell at the time it is generated. If the cell is low on energy, then glucose 6-phosphate will travel down the glycolytic pathway, eventually yielding two molecules of adenosine triphosphate. If the cell is in need of biosynthetic intermediates, glucose 6-phosphate will enter the pentose phosphate pathway, where it will undergo a series of reactions to yield riboses and/or NADPH, depending on cellular conditions.

If this reaction is taking place in the liver, the enzyme glucose 6-phosphatase can also catalyze the conversion of glucose 6-phosphate to glucose, which can leave the liver for use in other cells. Muscle cells, however, lack glucose 6-phosphatase, so they cannot share their glycogen stores with the rest of the body.

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