Uridine (
symbol
A symbol is a mark, Sign (semiotics), sign, or word that indicates, signifies, or is understood as representing an idea, physical object, object, or wikt:relationship, relationship. Symbols allow people to go beyond what is known or seen by cr ...
U or Urd) is a glycosylated
pyrimidine
Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The oth ...
analog containing
uracil
Uracil () (nucleoside#List of nucleosides and corresponding nucleobases, symbol U or Ura) is one of the four nucleotide bases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via ...
attached to a
ribose
Ribose is a simple sugar and carbohydrate with molecular formula C5H10O5 and the linear-form composition H−(C=O)−(CHOH)4−H. The naturally occurring form, , is a component of the ribonucleotides from which RNA is built, and so this comp ...
ring (or more specifically, a
ribofuranose) via a β-N
1-
glycosidic bond. The analog is one of the five standard
nucleosides
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 nucleotide ...
which make up
nucleic acids
Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic a ...
, the others being
adenosine
Adenosine (symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9- glycosidic bond. Adenosine is one of the four nucleoside build ...
,
thymidine
Thymidine (nucleoside#List of nucleosides and corresponding nucleobases, symbol dT or dThd), also known as deoxythymidine, deoxyribosylthymine, or thymine deoxyriboside, is a pyrimidine nucleoside, deoxynucleoside. Deoxythymidine is the DNA nuc ...
,
cytidine and
guanosine. The five nucleosides are
commonly abbreviated to their symbols, U, A, dT, C, and G, respectively. However, thymidine is more commonly written as 'dT' ('d' represents 'deoxy') as it contains a 2'-deoxyribofuranose moiety rather than the
ribofuranose ring found in uridine. This is because thymidine is found in
deoxyribonucleic acid (DNA) and usually not in
ribonucleic acid
Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins ( messenger RNA). RNA and deoxyr ...
(RNA). Conversely, uridine is found in RNA and not DNA. The remaining three nucleosides may be found in both RNA and DNA. In RNA, they would be represented as A, C and G whereas in DNA they would be represented as dA, dC and dG.
Biosynthesis
Uridine is widely produced in nature as
uridine monophosphate
Uridine monophosphate (UMP), also known as 5′-uridylic acid ( conjugate base uridylate), is a nucleotide that is used as a monomer in RNA. It is an ester of phosphoric acid with the nucleoside uridine. UMP consists of the phosphate group, th ...
(uridylate) by
de novo synthesis by the
decarboxylation of
orotidylate, which is catalyzed by
orotidylate decarboxylase. The orotidylate is produced from
orotate, which is combined with
5-phosphoribosyl-1-pyrophosphate (PRPP) to form
orotidylate by
pyrimidine phosphoribosyltransferase. PRPP is created from
ribose-5-phosphate by a further phosphorylation, serving as an energetic molecule to drive the reaction forward, while orotate is generated in several steps from
carbamoyl phosphate and
aspartate.
Dietary sources
Uridine is regarded as a non-essential nutrient, as it is produced by the human body as needed and supplementation is not generally recommended, though it has been explored for specific applications.
Some foods that contain uridine in the form of RNA are listed below. Although claimed that virtually none of the uridine in this form is bioavailable "since – as shown by Handschumacher's Laboratory at
Yale School of Medicine
The Yale School of Medicine is the medical school of Yale University, a private research university in New Haven, Connecticut. It was founded in 1810 as the Medical Institution of Yale College and formally opened in 1813. It is the sixth-oldest m ...
in 1981 – it is destroyed in the liver and gastrointestinal tract, and no food, when consumed, has ever been reliably shown to elevate blood uridine levels'. This is contradicted by Yamamoto et al., plasma uridine levels rose 1.8-fold 30 minutes after beer ingestion, suggesting, at the very least, conflicting data. On the other hand,
ethanol
Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
on its own (which is present in beer) increases uridine levels, which may explain the raise of uridine levels in the study by Yamamoto et al.
In infants consuming mother's milk or commercial infant formulas, uridine is present as its monophosphate, UMP, which is both bioavailable and able to enter the circulation from the digestive tract.
*goat's and sheep's milk and milk products
* Sugarcane extract
* Tomatoes (0.5 to 1.0 g uridine per kilogram dry weight)
* Brewer's
yeast
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...
(1.7% uridine by dry weight)
* Beer
*
Broccoli
Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the Brassicaceae, cabbage family (family Brassicaceae, genus ''Brassica'') whose large Pseudanthium, flowering head, plant stem, stalk and small associated leafy gre ...
*
Organ meats
Offal (), also called variety meats, pluck or organ meats, is the internal organs of a butchered animal. Offal may also refer to the by-products of milled grains, such as corn or wheat.
Some cultures strongly consider offal consumption to be ...
(liver, pancreas, etc.)
Consumption of RNA-rich foods may lead to high levels of
purines
Purine is a heterocyclic compound, heterocyclic aromatic organic compound that consists of two rings (pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which inc ...
(adenine and guanosine) in blood. High levels of purines are known to increase
uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the Chemical formula, formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the meta ...
production and may aggravate or lead to conditions such as
gout
Gout ( ) is a form of inflammatory arthritis characterized by recurrent attacks of pain in a red, tender, hot, and Joint effusion, swollen joint, caused by the deposition of needle-like crystals of uric acid known as monosodium urate crysta ...
.
Harvard researchers report that omega-3 fatty acids and uridine, two substances in foods such as fish, walnuts, molasses, and sugar beets, prevented depression in rats as effectively as antidepressant drugs. "Giving rats a combination of uridine and omega-3 fatty acids produced immediate effects that were indistinguishable from those caused by giving the rats standard antidepressant medications," said lead author of the study William Carlezon, director of McLean's Behavioral Genetics Laboratory.
Galactose glycolysis
Uridine plays a role in the
glycolysis
Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...
pathway of
galactose
Galactose (, ''wikt:galacto-, galacto-'' + ''wikt:-ose#Suffix 2, -ose'', ), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweetness, sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epime ...
.
There is no
catabolic
Catabolism () is the set of metabolic pathways that breaks down molecules into smaller units that are either oxidized to release energy or used in other anabolic reactions. Catabolism breaks down large molecules (such as polysaccharides, lipi ...
process to metabolize galactose. Therefore, galactose is converted to
glucose
Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...
and metabolized in the common glucose pathway. Once the incoming galactose has been converted into
galactose 1-phosphate (Gal-1-P), it is involved in a reaction with
UDP-glucose, a glucose molecule bonded to
uridine diphosphate (UDP). This process is catalyzed by the enzyme
galactose-1-phosphate uridyl transferase and transfers the UDP to the galactose molecule. The end result is UDP-galactose and glucose-1-phosphate. This process is continued to allow the proper glycolysis of galactose.
See also
*
Deoxyuridine monophosphate
*
Pseudouridine
*
Uridine monophosphate
Uridine monophosphate (UMP), also known as 5′-uridylic acid ( conjugate base uridylate), is a nucleotide that is used as a monomer in RNA. It is an ester of phosphoric acid with the nucleoside uridine. UMP consists of the phosphate group, th ...
References
{{Purinergics
Nucleosides
Pyrimidinediones
Antidepressants
Hydroxymethyl compounds