an enzyme of the transferase class that plays an important part in carbohydrate metabolism. Phosphoglucomutase catalyzes what is outwardly an intramolecular transfer of phosphate during the formation of glucose-6-phosphate from glucose-1-phosphate during glycolysis. The transfer, which occurs in the reaction following the phosphorolysis of glycogen, is as follows:

Phosphate is transferred from carbon atom 1 in one glucose molecule to carbon atom 6 in another molecule; glucose-1,6-diphos-phate acts as a coenzyme of the reaction, which requires the presence of Mg²⁺ ions. In the reaction, the phosphorylated form of phosphoglucomutase transfers the phosphate to carbon atom 6 of glucose-1-phosphate, forming glucose-1,6-diphosphate. The de-phosphorylated phosphoglucomutase then takes on the phosphate group at carbon atom 1 of glucose-1,6-diphosphate. Thus, glucose-6-phosphate is formed, and the enzyme again assumes its phosphorylated form. Glucose-1,6-diphosphate may also be formed by means of the kinase-catalyzed reaction

glucose-1-phosphate + adenosine triphosphate
→ glucose-1, 6-diphosphate + adenosine diphosphate

Phosphoglucomutase is widely distributed in plant, animal, and microbe cells; within the cell, it is located in the cytoplasm. The enzyme is obtained from various sources in a highly purified form; a protein, it has a molecular weight of 60,000–112,000. Phosphoglucomutase may be present in an organism in a number of different forms. Known as isoenzymes, these forms are similar with regard to protein activity. Characteristic sets of isoenzymes of phosphoglucomutase have been discovered in the erythrocytes, liver, kidneys, muscles, and placenta of humans. Phosphoglucomutase contains a residue of serine that is necessary for catalytic activity.