Phosphorylase
Phosphorylase | |||||||||
---|---|---|---|---|---|---|---|---|---|
![]() | |||||||||
Identifiers | |||||||||
EC no. | 2.4.1.1 | ||||||||
CAS no. | 9035-74-9 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
|
In biochemistry, phosphorylases are enzymes that catalyze the addition of a phosphate group from an inorganic phosphate (phosphate+hydrogen) to an acceptor.
- 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 it as the first phosphorylase.[1]
Function
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 |
---|---|---|---|
Phosphorylase | Transferase (EC 2.4 and EC 2.7.7) | A-B + H-OP ⇌ A-OP + H-B | transfer group = A = glycosyl- group or nucleotidyl- group |
Phosphatase | Hydrolase (EC 3) | P-B + H-OH ⇌ P-OH + H-B | |
Kinase | Transferase (EC 2.7.1-2.7.4) | P-B + H-A ⇌ P-A + H-B | transfer group = P |
P = phosphonate group, OP = phosphate group, H-OP or P-OH = inorganic phosphate |
Types
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)
- Enzymes that have phosphorolytic 3' to 5' exoribonuclease activity (break phosphodiester bond)
- RNase PH
- Polynucleotide Phosphorylase (PNPase)
- Enzymes that have phosphorolytic 3' to 5' exoribonuclease activity (break phosphodiester bond)
All known phosphorylases share catalytic and structural properties.[2]
Activation
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.
Pathology
Some disorders are related to phosphorylases:
- Glycogen storage disease type V - muscle glycogen
- Glycogen storage disease type VI - liver glycogen
See also
References
External links
- Muscle phosphorylase deficiency - McArdle's Disease Website
- Phosphorylases at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- v
- t
- e
phosphotransferase/kinase
(PO4)
2.7.1: OH acceptor | |
---|---|
2.7.2: COOH acceptor | |
2.7.3: N acceptor | |
2.7.4: PO4 acceptor |
(P2O7)
(PO4-nucleoside)
Polymerase |
| ||||
---|---|---|---|---|---|
Phosphorolytic 3' to 5' exoribonuclease | |||||
Nucleotidyltransferase | |||||
Guanylyltransferase | |||||
Other |
Phosphatidyltransferases | |
---|---|
Glycosyl-1-phosphotransferase |
(PO4; protein acceptor)
2.7.10: protein-tyrosine |
|
---|---|
2.7.11: protein-serine/threonine |
|
2.7.12: protein-dual-specificity |
|
2.7.13: protein-histidine |