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Inosinic acid
Identifiers
CAS number	131-99-7 Y
PubChem	8582
MeSH	Inosine+monophosphate
Properties
Molecular formula	C10H13N4O8P
Molar mass	348.206 g/mol
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Inosinic acid or inosine monophosphate (IMP) is a nucleoside monophosphate. Inosinic acid is important in metabolism. It is the ribonucleotide of hypoxanthine and the first nucleotide formed during the synthesis of purine. It is formed by the deamination of adenosine monophosphate, and is hydrolysed from inosine.

Important derivatives of inosinic acid include purine nucleotides found in nucleic acids and adenosine triphosphate, which is used to store chemical energy in muscle and other tissues.

In the food industry, inosinic acid and its salts such as disodium inosinate are used as flavour enhancers.

[edit] Inosinate synthesis

The inosinate synthesis is complex and it begins with a 5-phosphoribosyl-1-pyrophosphate (PRPP). In the first step, an amino group given by glutamine is attached at carbon 1 of PRPP. The resulting molecule is 5-phosphoribosylamine, which is highly unstable, with a half-life of 30 seconds at physiologic pH. 5-phosphoribosylamine gains an amino acid (glycine) and it becomes glycinamide ribonucleotide. Then, N10-formyltetrahydrofolate (THF) transfers a formil group to glycinamide ribonucleotide to form formyilglycinamide ribonucleotide.

This figure shows the pathway described below: IMP synthesis.

Using an ATP molecule, ammonia is added to the compound to become formylglycinamidine ribonucleotide. Another ATP molecule causes an intermolecular reaction that produces an imidazole ring (5-aminoimidazole ribonucleotide).

The next step of the pathway is adding bicarbonate to make carboxyaminoimidazole ribonucleotide by using ATP (it only happens in fungi and bacteria; high eukaryotes simply add CO2 to form the ribonucleotide). Then, the imidazole’s carboxylate group phosphatises and adds aspartate.

As we have just seen, a six-step process links glycine, formiate, bicarbonate, ammonia and aspartate to lead to an intermediate which contains almost all the required atoms to synthesize a purine ring. This intermediate removes fumarate, and a second formyl group from THF is added. The compound gets cycled and forms inosinate after a sort of intermolecular reactions. Inosinate is the first intermediate in this synthesis pathway to have a whole purine ring.

Enzymes taking part in IMP synthesis constitute a multienzyme complex in the cell. Evidences demonstrate that there are multifunctional enzymes, and some of them catalyze non-sequential steps in the pathway.

[edit] Adenylate (AMP) and guanylate (GMP) take form from inosinate

Within a few steps inosinate becomes AMP or GMP. Both compounds are RNA nucleotides. AMP differs from inosinate by changing oxygen from IMP carbon 6 to an amino group, using GTP and aspartate. These reactions are catalyzed by adenylsuccinate-synthetase. GMP is formed by the inosinate oxidation to xanthylate (XMP), and afterwards adds an amino group on carbon 2. Hydrogen acceptor on inosinate oxidation is NAD+. Finally, carbon 2 gains the amino group by spending an ATP molecule (which becomes AMP+2Pi). While AMP synthesis requires GTP, GMP synthesis uses ATP. That difference offers an important regulation possibility.

Glutamine-PRPP-amidotransferase

[edit] Inosinate takes part on the regulation of purine nucleotides biosynthesis

Inosinate and many other molecules inhibit the synthesis of 5-phosphorybosilamine from 5-phosphoribosyl-1-pyrophosphate (PRPP), disabling the enzyme which catalyzes the reaction: glutamine-5-phosphoribosyl-1-pyrophosphate-amidotransferase. In other words, when inosinate high levels are given, this enzyme inhibits and, as a consequence, inosinate levels decrease. This means that adenylate and guanylate are not produced, as they are, as we have just seen, a product of the inosinate pathway.

If adenilate and guanylate are not produced RNA synthesis cannot be completed because of the lack of these two important RNA nucleotides.

[edit] Applications

Inosinate can be manufactured into various compounds with the aid of genetically modified organisms: disodium inosinate E 631, dipotassium inosinate E 632 and dicalcium inosinate E 633. These three compounds are used as flavour enhancers with a comparatively high effectiveness. They are mostly used in soups, sauces and seasonings for the intensification and balance of meat taste.

[edit] Bibliography

Berg, Jeremy M.; Bioquímica; Editorial Reverté; 6ena edició; Barcelona 2007.

Nelson, David L.; Principles of biochemistry; Editorial W.H Freeman and Company; 4th edition; New York 2005.