Phosphoribosylamine (PRA) is a biochemical intermediate in the formation of
purine
Purine is a 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 include substituted purines ...
nucleotides
Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules with ...
via
inosine
Inosine is a nucleoside that is formed when hypoxanthine is attached to a ribose ring (also known as a ribofuranose) via a β-N9- glycosidic bond. It was discovered in 1965 in analysis of RNA transferase.
Inosine is commonly found in tRNAs and is ...
-5-monophosphate, and hence is a building block for
DNA and
RNA.
The vitamins
thiamine
Thiamine, also known as thiamin and vitamin B1, is a vitamin, an essential micronutrient, that cannot be made in the body. It is found in food and commercially synthesized to be a dietary supplement or medication. Phosphorylated forms of thi ...
and
cobalamin
Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. ...
also contain fragments derived from PRA.
:
![Phosphoribosyl pyrophosphate](https://upload.wikimedia.org/wikipedia/commons/2/26/Phosphoribosyl_pyrophosphate.svg)
It is the product of the enzyme
amidophosphoribosyltransferase which attaches
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
from
glutamine
Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...
to
phosphoribosyl pyrophosphate
Phosphoribosyl pyrophosphate (PRPP) is a pentose phosphate. It is a biochemical intermediate in the formation of purine nucleotides via inosine-5-monophosphate, as well as in pyrimidine nucleotide formation. Hence it is a building block for DN ...
(PRPP) at its
anomeric carbon:
[
: + → + + PPi
The biosynthesis pathway next combines PRA with ]glycine
Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
in a process driven by ATP giving glycineamide ribonucleotide
Glycineamide ribonucleotide (or GAR) is a biochemical intermediate in the formation of purine nucleotides via inosine-5-monophosphate, and hence is a building block for DNA and RNA. The vitamins thiamine and cobalamin also contain fragments deri ...
(GAR). The enzyme phosphoribosylamine—glycine ligase
''Phosphoribosylamine—glycine ligase'', also known as glycinamide ribonucleotide synthetase (GARS), () is an enzyme that catalyzes the chemical reaction
:ATP + 5-phospho-D-ribosylamine + glycine \rightleftharpoons ADP + phosphate +
which i ...
catalyses the reaction forming an amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...
bond:
: + + ATP → + ADP + Pi
See also
* 5-Aminoimidazole ribotide
* Purine metabolism
Purine metabolism refers to the metabolic pathways to synthesize and break down purines that are present in many organisms.
Biosynthesis
Purines are biologically synthesized as nucleotides and in particular as ribotides, i.e. bases attached to r ...
References
{{Nucleotide metabolism intermediates
Organophosphates
Amino sugars