Phosphorylase

Phosphorylase
Identifiers
EC no.2.4.1.1
CAS no.9035-74-9
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
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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.

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:

All known phosphorylases share catalytic and structural properties.

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:

See also



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