Phosphoglycerate mutase

This enzyme is not to be confused with Bisphosphoglycerate mutase which catalyzes the conversion of 1,3-bisphosphoglycerate to 2,3-bisphosphoglycerate.

Phosphoglycerate mutase (PGM) is an enzyme that catalyzes step 8 of glycolysis. It catalyzes the internal transfer of a phosphate group from C-3 to C-2 which results in the conversion of 3-phosphoglycerate (3PG) to 2-phosphoglycerate (2PG) through a 2,3-bisphosphoglycerate intermediate.

Mechanism

PGM is an isomerase enzyme, effectively transferring a phosphate group (PO₃^2-) from the C-3 carbon of 3-phosphoglycerate to the C-2 carbon forming 2-phosphoglycerate. The reaction involves two separate phosphoryl groups and the ending phosphate on the 2-carbon is not the same phosphate removed from the 3-carbon.
In the enzyme's initial state, the active site contains a phosphohistidine complex formed by phosphorylation of a specific histidine residue. When 3-phosphoglycerate enters the active site, the phosphohistidine complex is positioned as to facilitate transfer of phosphate from enzyme to substrate C-2 creating a 2,3-bisphosphoglycerate intermediate.
Dephosphorylation of the enzyme histidine actuates a local allosteric change in enzyme configuration which now aligns the substrates 3-C phosphate group with enzyme active site histidine and facilitates phosphate transfer returning the enzyme to its initial phosphorylated state and releasing product 2-phosphoglycerate.

Reaction Summary

3PG + P-Enzyme → 2,3BPG + Enzyme → 2PG + P-Enzyme

   3-phosphoglycerate         intermediate          2-phosphoglycerate

ΔG°′=+1.1kcal/mol

• 

  3PG

• 

  2,3BPG

• 

  2PG

Isozymes

Phosphoglycerate mutase exists primarily as a dimer of two either identical or closely related subunits of about 32kDa. The enzyme is found in organisms as simple as yeast through homo sapiens and its structure is highly conserved throughout. (Yeast PGM≈74% conserved vs mammal form).
In mammals, the enzyme subunits appear to be either a muscle-derived form (m-type) or other tissue (b-type for brain where the b-isozyme was originally isolated). Existing as a dimer, the enzyme then has 3 isozymes depending on which subunit forms makeup the whole molecule (mm, bb or mb). The mm-type is found mainly in smooth muscle almost exclusively. The mb-isozyme is found in cardiac and skeletal muscle and the bb-type is found in the rest of tissues. While all three isozymes may be found in any tissue, the above distributions are based on prevalence in each.

m-muscle derived

b-brain derived

Interactive pathway map

Click on genes, proteins and metabolites below to link to respective articles. ^{[§ 1]}

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Glycolysis and Gluconeogenesis edit

1. ↑ The interactive pathway map can be edited at WikiPathways: "GlycolysisGluconeogenesis_WP534". 

Regulation

Phosphoglycerate mutase has a small positive Gibbs free energy and this reaction proceeds easily in both directions. Since it is a reversible reaction, it is not the site of major regulation mechanisms or regulation schemes for the glycolytic pathway.

Deficiency

In humans the PGAM2 gene which encodes this enzyme is located on the short arm of chromosome 7. Dysfunction in the activity of phosphoglycerate mutase is a rare autosomal recessive genetic disorder with symptoms ranging from mild to moderate, is not thought life-threatening and can be managed with changes in lifestyle. This presents as a metabolic myopathy and is one of the many forms of syndromes formerly referred to as muscular dystrophy.

Onset is generally noted as childhood to early adult though some who may be mildly affected by the disorder may not know they have it. Patients with PGAM deficiency are usually asymptomatic, except when they engage in brief, strenuous efforts which may trigger myalgias, cramps, muscle necrosis and myoglobinuria.^[1] An unusual pathologic feature of PGAM deficiency is the association with tubular aggregates. The symptoms are an intolerance to physical exertion or activity, cramps and muscle pain. Permanent weakness is rare. The disease is not progressive and has an excellent prognosis.

Human proteins containing this domain

BPGM; PFKFB1; PFKFB2; PFKFB3; PFKFB4; PGAM1; PGAM2; PGAM4; PGAM5; STS1; UBASH3A;

References

External links

• Phosphoglycerate Mutase at the US National Library of Medicine Medical Subject Headings (MeSH)