Phosphorylases are enzymes that catalyze the addition of a phosphate group from an inorganic phosphate (phosphate+hydrogen) to an acceptor.
|PDB structures||RCSB PDB PDBe PDBsum|
- A-B + P ⇌ A + P-B
They include allosteric enzymes that catalyze the production of glucose-1-phosphate from a glucan such as glycogen, starch or maltodextrin. Phosphorylase is also a common name used for glycogen phosphorylase in honor of Earl W. Sutherland Jr. who in the late 1930s discovered the first phosphorylase.
Phosphorylases should not be confused with phosphatases, which remove phosphate groups. In more general terms, phosphorylases are enzymes that catalyze the addition of a phosphate group from an inorganic phosphate (phosphate + hydrogen) to an acceptor, not to be confused with a phosphatase (a hydrolase) or a kinase (a phosphotransferase). A phosphatase removes a phosphate group from a donor using water, whereas a kinase transfers a phosphate group from a donor (usually ATP) to an acceptor.
|Enzyme name||Enzymes class||Reaction||Notes|
(EC 2.4 and EC 2.7.7)
|A-B + H-OP ⇌ A-OP + H-B||transfer group = A = glycosyl- group or|
|P-B + H-OH ⇌ P-OH + H-B|
|P-B + H-A ⇌ P-A + H-B||transfer group = P|
|P = phosphonate group, OP = phosphate group, H-OP or P-OH = inorganic phosphate|
The phosphorylases fall into the following categories:
- Glycosyltransferases (EC 2.4)
- Enzymes that break down glucans by removing a glucose residue (break O-glycosidic bond)
- Enzymes that break down nucleosides into their constituent bases and sugars (break N-glycosidic bond)
- Purine nucleoside phosphorylase (PNPase)
- Nucleotidyltransferases (EC 2.7.7)
All known phosphorylases share catalytic and structural properties .
Phosphorylase a is the more active R form of glycogen phosphorylase that is derived from the phosphorylation of the less active R form, phosphorylase b with associated AMP. The inactive T form is either phosphorylated by phosphoylase kinase and inhibited by glucose, or dephosphorylated by phosphoprotein phosphatase with inhibition by ATP and/or glucose 6-phosphate. Phosphorylation requires ATP but dephosphorylation releases free inorganic phosphate ions.
Some disorders are related to phosphorylases:
- Lehninger Principles of Biochemistry 5th ed. pg. 603
- Muscle phosphorylase deficiency - McArdle's Disease Website
- Phosphorylases at the US National Library of Medicine Medical Subject Headings (MeSH)
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