Inosinic acid or inosine monophosphate (IMP) is a
nucleotide
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 ...
(that is, a
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 nucleotid ...
monophosphate). Widely used as a flavor enhancer, it is typically obtained from chicken byproducts or other
meat industry
The meat industry are the people and companies engaged in modern industrialized livestock agriculture for the production, packing, preservation and marketing of meat (in contrast to dairy products, wool, etc.). In economics, the meat industry is ...
waste. Inosinic acid is important in
metabolism
Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
. It is the
ribonucleotide
In biochemistry, a ribonucleotide is a nucleotide containing ribose as its pentose component. It is considered a molecular precursor of nucleic acids. Nucleotides are the basic building blocks of DNA and RNA. Ribonucleotides themselves are basic mo ...
of
hypoxanthine
Hypoxanthine is a naturally occurring purine derivative. It is occasionally found as a constituent of nucleic acids, where it is present in the anticodon of tRNA in the form of its nucleoside inosine. It has a tautomer known as 6-hydroxypurine. Hyp ...
and the first nucleotide formed during the synthesis 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. It can also be formed by the
deamination
Deamination is the removal of an amino group from a molecule. Enzymes that catalysis, catalyse this reaction are called deaminases.
In the human body, deamination takes place primarily in the liver; however, it can also occur in the kidney. In s ...
of
adenosine monophosphate
Adenosine monophosphate (AMP), also known as 5'-adenylic acid, is a nucleotide. AMP consists of a phosphate group, the sugar ribose, and the nucleobase adenine. It is an ester of phosphoric acid and the nucleoside adenosine. As a substituent it t ...
by
AMP deaminase. It can be
hydrolysed to
inosine.
The enzyme deoxyribonucleoside triphosphate pyrophosphohydrolase, encoded by YJR069C in ''
Saccharomyces cerevisiae
''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...
'' and containing (d)ITPase and (d)XTPase activities, hydrolyzes
inosine triphosphate (ITP) releasing
pyrophosphate
In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate () and tetrasodium pyrophosphate (), among others. Often pyrophosphates a ...
and IMP.
Important derivatives of inosinic acid include the purine nucleotides found in
nucleic acid
Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...
s and
adenosine triphosphate
Adenosine triphosphate (ATP) is a nucleoside triphosphate that provides energy to drive and support many processes in living cell (biology), cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known ...
, which is used to store
chemical energy
Chemical energy is the energy of chemical substances that is released when the substances undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, Schmidt-Rohr, K. (20 ...
in
muscle
Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
and other tissues.
In the food industry, inosinic acid and its
salts
In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...
such as
disodium inosinate are used as
flavor enhancer
A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive that is used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of t ...
s. It is known as
E number
E numbers, short for Europe numbers, are codes for substances used as food additives, including those found naturally in many foods, such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...
reference E630.
Inosinate synthesis
The inosinate synthesis is complex, beginning with a
5-phosphoribosyl-1-pyrophosphate (PRPP).
Enzymes
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...
taking part in IMP synthesis constitute a multienzyme complex in the cell. Evidence demonstrates that there are multifunctional enzymes, and some of them catalyze non-sequential steps in the pathway.
Synthesis of other purine nucleotides
Within a few steps inosinate becomes
AMP or
GMP.
Both compounds are
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 ...
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 ...
.
AMP differs from inosinate by the replacement of IMP's carbon-6 carbonyl with an amino group. The interconversion of AMP and IMP occurs as part of the
purine nucleotide cycle
The Purine Nucleotide Cycle is a metabolic pathway in protein metabolism requiring the amino acids aspartate and glutamate. The cycle is used to regulate the levels of adenine nucleotides, in which ammonia and fumarate are generated. AMP conv ...
.
[Voet, D, Voet, J. G., Biochemistry (3rd Edition), John Wiley & Sons, Inc., 2004, pg 1095] GMP is formed by the inosinate oxidation to
xanthylate
Xanthosine monophosphate (xanthylate) is an intermediate in purine metabolism. It is a ribonucleoside monophosphate. It is formed from IMP via the action of IMP dehydrogenase, and it forms GMP via the action of GMP synthase. Also, XMP can be ...
(XMP), and afterwards adds an amino group on carbon 2. Hydrogen acceptor on inosinate oxidation is
NAD+
Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an ade ...
. 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.
Regulation of purine nucleotide biosynthesis
Inosinate and many other molecules inhibit the synthesis of 5-
phosphoribosylamine from 5-phosphoribosyl-1-pyrophosphate (PRPP), disabling the enzyme that catalyzes the reaction: glutamine-5-phosphoribosyl-1-pyrophosphate-amidotransferase. In other words, when levels of inosinate are high, glutamine-5-phosphoribosyl-1-pyrophosphate-amidotransferase is inhibited, and, as a consequence, inosinate levels decrease. Also, as a result, adenylate and guanylate are not produced, which means that RNA synthesis cannot be completed because of the lack of these two important RNA nucleotides.
Applications
Inosinic acid can be converted into various
salts
In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...
including
disodium inosinate (E631),
dipotassium inosinate (E632), and
calcium inosinate (E633). These three compounds are used as
flavor enhancer
A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive that is used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of t ...
s for the basic taste
umami
Umami ( from ), or savoriness, is one of the five basic tastes. It is characteristic of broths and cooked meats.
People taste umami through taste receptors that typically respond to glutamates and nucleotides, which are widely present in me ...
or savoriness with a comparatively high effectiveness. They are mostly used in soups, sauces, and seasonings for the intensification and balance of the flavor of meat.
See also
References
Further reading
* 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.
{{DEFAULTSORT:Inosinic Acid
Food additives
Organic acids
Flavor enhancers
Nucleotides
Purines
E-number additives