Neuraminic acid (5-amino-3,5-dideoxy-D-''glycero''-D-''galacto''-non-2-ulosonic acid) is an

acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

(in particular ulosonic) amino sugar with a backbone formed by nine

carbon atom Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—its atom making four electrons available to form covalent bond, covalent chemical bonds. It belongs to gro ...

s. Although 9-carbon sugars do not occur naturally, neuraminic acid may be regarded as a theoretical 9-carbon

ketose A ketose is a monosaccharide containing one ketone group per molecule. The simplest ketose is dihydroxyacetone, which has only three carbon atoms. It is the only ketose with no optical activity. All monosaccharide ketoses are reducing sugars, be ...

in which the first link of the chain (the –CH₂OH at position 1) is

oxidised Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

into a

carboxyl group In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

(–C(=O)OH), the

hydroxyl group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy g ...

at position 3 is deoxidised (oxygen is removed from it), and the hydroxyl group at position 5 is substituted with an

amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such a ...

(–NH₂). Neuraminic acid may also be visualized as the product of an aldol-condensation of

pyruvic acid Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...

and D-

mannosamine D-Mannosamine (2-amino-2-deoxymannose) is a hexosamine derivative of mannose. See also * Neuraminic acid Neuraminic acid (5-amino-3,5-dideoxy-D-''glycero''-D-''galacto''-non-2-ulosonic acid) is an acidic (in particular ulosonic) amino ...

(2-amino-2-deoxy-mannose). Neuraminic acid does not occur naturally, but many of its derivatives are found widely distributed in animal tissues and in bacteria, especially in

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

s and

ganglioside A ganglioside is a molecule composed of a glycosphingolipid (ceramide and oligosaccharide) with one or more sialic acids (e.g. ''N''-acetylneuraminic acid, NANA) linked on the sugar chain. NeuNAc, an acetylated derivative of the carbohydrate sia ...

s. The ''N''- or ''O''-substituted derivatives of neuraminic acid are collectively known as

sialic acid Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone. The term "sialic acid" (from the Greek for saliva, - ''síalon'') was first introduced by Swedish biochemist Gunnar Blix in 1952. The most common member of this gr ...

s, the predominant form in mammalian cells being ''N''-acetylneuraminic acid. The amino group bears either an acetyl or a glycolyl group. The hydroxyl substituents may vary considerably: acetyl, lactyl, methyl, sulfate and phosphate groups have been found. The name "neuraminic acid" was introduced by German scientist E. Klenk in 1941, in reference to the brain lipids from which it was derived as a cleavage product.Klenk, E. 1941. Neuraminsäure, das Spaltprodukt eines neuen Gehirnlipoids. ''Zeitschr. f. Physiol. Chem.'' 1941; 268:50-58. The

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

symbol used for neuraminic acid is Neu, and the residue is typically found with additional chemical modifications in biological systems. As a family, these residues are known as

sialic acids Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone. The term "sialic acid" (from the Greek for saliva, - ''síalon'') was first introduced by Swedish biochemist Gunnar Blix in 1952. The most common member of this ...

. For example, ''N''-acetylneuraminic acid, Neu5Ac, is typical in human glycoproteins. Among their many biological functions, these structures are substrates for

neuraminidase Exo-α-sialidase (EC 3.2.1.18, sialidase, neuraminidase; systematic name acetylneuraminyl hydrolase) is a glycoside hydrolase that cleaves the glycosidic linkages of neuraminic acids: : Hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)- glycos ...

enzymes which cleave neuraminic acid residues. Human

flu Influenza, commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptom ...

viruses have a neuraminidase enzyme, signified in the name "H#N#", where the H refers to an

isoform A protein isoform, or "protein variant", is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences. While many perform the same or similar biological roles, some isof ...

hemagglutinin In molecular biology, hemagglutinins (or ''haemagglutinin'' in British English) (from the Greek , 'blood' + Latin , 'glue') are receptor-binding membrane fusion glycoproteins produced by viruses in the ''Paramyxoviridae'' family. Hemagglutinins ar ...

and N refers to an isoform of

viral neuraminidase Viral neuraminidase is a type of neuraminidase found on the surface of influenza viruses that enables the virus to be released from the host cell. Neuraminidases are enzymes that cleave sialic acid (also called neuraminic acid) groups from ...

References

{{Carbohydrates Amino sugars Monosaccharide derivatives Sugar acids de:Neuraminsäure