Phosphorylase
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Phosphorylase

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 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:

All known phosphorylases share catalytic and structural properties [1].

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

References

  1. ^ Lehninger Principles of Biochemistry 5th ed. pg. 603

External links



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Phosphorylase
 



 



 
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