In
biochemistry
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology ...
, phosphorylases are
enzymes that
catalyze the addition of a
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
group from an
inorganic
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemis ...
phosphate (phosphate+
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
) to an acceptor.
:A-B + P A + P-B
They include
allosteric enzymes that catalyze the production of
glucose-1-phosphate from a
glucan
A glucan is a polysaccharide derived from D-glucose, linked by glycosidic bonds. Glucans are noted in two forms: alpha glucans and beta glucans. Many beta-glucans are medically important. They represent a drug target for antifungal medications ...
such as
glycogen
Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body.
Glycogen functions as one o ...
,
starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...
or
maltodextrin
Maltodextrin is a polysaccharide that is used as a food ingredient. It is produced from vegetable starch by partial hydrolysis and is usually found as a white hygroscopic spray-dried powder. Maltodextrin is easily digestible, being absorbed ...
.
Phosphorylase is also a common name used for
glycogen phosphorylase
Glycogen phosphorylase is one of the phosphorylase enzymes (). Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Glycogen phosphor ...
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
In biochemistry, a phosphatase is an enzyme that uses water to cleave a phosphoric acid monoester into a phosphate ion and an alcohol. Because a phosphatase enzyme catalyzes the hydrolysis of its substrate, it is a subcategory of hydrolases. Pho ...
, 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
In biochemistry, a phosphatase is an enzyme that uses water to cleave a phosphoric acid monoester into a phosphate ion and an alcohol. Because a phosphatase enzyme catalyzes the hydrolysis of its substrate, it is a subcategory of hydrolases. Ph ...
(a
hydrolase
Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are es ...
) or a
kinase
In biochemistry, a kinase () is an enzyme that catalysis, catalyzes the transfer of phosphate groups from High-energy phosphate, high-energy, phosphate-donating molecules to specific Substrate (biochemistry), substrates. This process is known as ...
(a
phosphotransferase
Phosphotransferases are a category of enzymes ( EC number 2.7) that catalyze phosphorylation reactions. The general form of the reactions they catalyze is:
:A-P + B \rightleftharpoons B-P + A
Where ''P'' is a phosphate group and A and B are the d ...
). 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.
Types
The phosphorylases fall into the following categories:
*Glycosyltransferases (EC 2.4)
**Enzymes that break down
glucan
A glucan is a polysaccharide derived from D-glucose, linked by glycosidic bonds. Glucans are noted in two forms: alpha glucans and beta glucans. Many beta-glucans are medically important. They represent a drug target for antifungal medications ...
s by removing a glucose residue (break ''O''-glycosidic bond)
***
glycogen phosphorylase
Glycogen phosphorylase is one of the phosphorylase enzymes (). Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Glycogen phosphor ...
***
starch phosphorylase Starch phosphorylase is a form of phosphorylase similar to glycogen phosphorylase, except that it acts upon starch instead of glycogen
Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, ...
***
maltodextrin phosphorylase
**Enzymes that break down
nucleoside
Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar ( ribose or 2'-deoxyribose) whereas a nucleoti ...
s into their constituent bases and sugars (break ''N''-glycosidic bond)
***
Purine nucleoside phosphorylase
Purine nucleoside phosphorylase, PNP, PNPase or inosine phosphorylase () is an enzyme that in humans is encoded by the ''NP'' gene. It catalyzes the chemical reaction
:purine nucleoside + phosphate \rightleftharpoons purine + alpha-D-ribose 1-p ...
(PNPase)
*Nucleotidyltransferases (EC 2.7.7)
**Enzymes that have phosphorolytic 3' to 5' exoribonuclease activity (break phosphodiester bond)
***
RNase PH
RNase PH is a tRNA nucleotidyltransferase, present in archaea and bacteria, that is involved in tRNA processing. Contrary to hydrolytic enzymes, it is a phosphorolytic enzyme, meaning that it uses inorganic phosphate as a reactant to cleave nuc ...
***
Polynucleotide Phosphorylase (PNPase)
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:
*
Glycogen storage disease type V - muscle glycogen
*
Glycogen storage disease type VI - liver glycogen
See also
*
Hydrolase
Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are es ...
References
External links
Muscle phosphorylase deficiency - McArdle's Disease Website*
Transferases
EC 2.4.1
{{2.4-enzyme-stub