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 1930's discovered the first phosphorylase. ^[1]

Function

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 phosphonate group from a donor using water, whereas a kinase transfers a phosphonate 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:

• Glycosyltranferases (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 [1].

Activation

Phosphorylase a is the active form of glycogen phosphorylase that is derived from the phosphorylation of the inactive form, phosphorylase b.

Pathology

Some disorders are related to phosphorylases:

• Glycogen storage disease type V - muscle glycogen
• Glycogen storage disease type VI - liver glycogen

References

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

See also

• Hydrolase

External links

• Muscle phosphorylase deficiency - McArdle's Disease Website
• MeSH Phosphorylases