phosphorylase
{{Short description|Class of enzymes}}
{{Infobox enzyme
| Name = Phosphorylase
| EC_number = 2.4.1.1
| CAS_number = 9035-74-9
| GO_code =
| image = 1z8d.jpg
| width = 270
| caption =
}}
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 {{eqm}} 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.{{cite book | vauthors = Nelson DL, Lehninger AL, Cox MM |title=Lehninger Principles of Biochemistry |date=2005 |publisher=W. H. Freeman |isbn=978-0-7167-4339-2 |page=603 |edition= 5th}}
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.
| class=wikitable
!Enzyme name !Enzymes class !Reaction !Notes | |||
| Phosphorylase | Transferase (EC 2.4 and EC 2.7.7) | A-B + H-OP {{eqm}} A-OP + H-B | transfer group = A = glycosyl- group or nucleotidyl- group |
| '
|Phosphatase | Hydrolase (EC 3) | P-B + H-OH {{eqm}} P-OH + H-B | |
| Kinase | Transferase (EC 2.7.1-2.7.4) | P-B + H-A {{eqm}} P-A + H-B | transfer group = P |
| colspan=4|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)
- glycogen phosphorylase
- starch phosphorylase
- maltodextrin phosphorylase
- 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)
All known phosphorylases share catalytic and structural properties.{{cite web | title = PROSITE documentation PDOC00095 [for PROSITE entry PS00102] | url = https://prosite.expasy.org/doc/PS00102 | work = PROSITE }}
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
{{Reflist}}
External links
- [http://mcardlesdisease.org Muscle phosphorylase deficiency - McArdle's Disease Website]
- {{MeshName|Phosphorylases}}
{{Kinases}}
{{Glycosyltransferases}}
{{Enzymes}}
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