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 puri ...
nucleotides
Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...
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
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
and
RNA
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 deoxyrib ...
.
The vitamins
thiamine
Thiamine, also known as thiamin and vitamin B1, is a vitamin – an Nutrient#Micronutrients, essential micronutrient for humans and animals. It is found in food and commercially synthesized to be a dietary supplement or medication. Phosp ...
and
cobalamin
Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. One of eight B vitamins, it serves as a vital cofactor (biochemistry), cofactor in DNA synthesis and both fatty acid metabolism, fatty acid and amino a ...
also contain fragments derived from PRA.
:

It is the product of the enzyme
amidophosphoribosyltransferase
Amidophosphoribosyltransferase (ATase), also known as glutamine phosphoribosylpyrophosphate amidotransferase (GPAT), is an enzyme responsible for catalyzing the conversion of 5-phosphoribosyl-1-pyrophosphate (PRPP) into 5-phosphoribosyl-1-amine ...
which attaches
ammonia
Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
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 Sugar phosphates, pentose phosphate. It is a biochemical intermediate in the formation of purine nucleotides via Inosinic acid, inosine-5-monophosphate, as well as in pyrimidine nucleotide formation. Hence ...
(PRPP) at its
anomeric carbon
In carbohydrate chemistry, a pair of anomers () is a pair of near-identical stereoisomers or diastereomers that differ at only the anomeric carbon, the carbon atom that bears the aldehyde or ketone functional group in the sugar's open-chain f ...
:
[
: + → + + 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. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...
in a process driven by ATP giving glycineamide ribonucleotide
Glycinamide 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 derived ...
(GAR). The enzyme phosphoribosylamine—glycine ligase
Phosphoribosylamine—glycine ligase, also known as glycinamide ribonucleotide synthetase (GARS), () is an enzyme that catalysis, catalyzes the chemical reaction
:ATP + 5-phospho-D-ribosylamine + glycine \rightleftharpoons ADP + phosphate +
w ...
catalyses the reaction forming an amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...
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