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]
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[edit]
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 [1].
Activation[edit]
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[edit]
Some disorders are related to phosphorylases:
- Glycogen storage disease type V - muscle glycogen
- Glycogen storage disease type VI - liver glycogen
See also[edit]
References[edit]
- ^ Lehninger Principles of Biochemistry 5th ed. pg. 603
https://en.wikipedia.org/wiki/Phosphorylase
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