Phosphorylase

Phosphorylase
Identifiers
EC number	2.4.1.1
CAS number	Template:CAS
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Search PMC articles PubMed articles NCBI proteins

Phosphorylases are enzymes that catalyze the addition of a phosphate group from an inorganic phosphate (phosphate+hydrogen) to an acceptor.

A-B + P $\rightleftharpoons$ 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.

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 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 $\rightleftharpoons$ A-OP + H-B	transfer group = A = glycosyl- group or nucleotidyl- group
Phosphatase	Hydrolase (EC 3)	P-B + H-OH $\rightleftharpoons$ P-OH + H-B
Kinase	Transferase (EC 2.7.1-2.7.4)	P-B + H-A $\rightleftharpoons$ 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:

• 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 [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

See also

• Hydrolase

External links

• Muscle phosphorylase deficiency - McArdle's Disease Website
• Phosphorylases at the US National Library of Medicine Medical Subject Headings (MeSH)