Neuraminic acid
Encyclopedia
Neuraminic acid is a 9-carbon monosaccharide
, a derivative of a ketononose
. Neuraminic acid may be visualized as the product of an aldol-condensation
product of pyruvic acid
and D-mannosamine
(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
s and ganglioside
s. The N- or O-substituted derivatives of neuraminic acid are collectively known as sialic acid
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..
The symbol commonly 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. For example, N-acetyl-neuraminic acid, Neu5Ac, is typical in human glycoproteins.
Among their many biological functions, these structures are substrates for neuraminidase
enzymes which cleave neuraminic acid residues. Human flu viruses have a neuraminidase enzyme, signified in the name "H#N#", where the H refers to an isoform of hemaglutinin and N refers to an isoform of viral neuraminidase
.
Monosaccharide
Monosaccharides are the most basic units of biologically important carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose , fructose , galactose, xylose...
, a derivative of a ketononose
Ketose
A ketose is a sugar containing one ketone group per molecule.With 3 carbon atoms, dihydroxyacetone is the simplest of all ketoses and is the only one having no optical activity. Ketoses can isomerize into an aldose when the carbonyl group is located at the end of the molecule...
. Neuraminic acid may be visualized as the product of an aldol-condensation
Aldol condensation
An aldol condensation is an organic reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by a dehydration to give a conjugated enone....
product of pyruvic acid
Pyruvic acid
Pyruvic acid is an organic acid, a ketone, as well as the simplest of the alpha-keto acids. The carboxylate ion of pyruvic acid, CH3COCOO−, is known as pyruvate, and is a key intersection in several metabolic pathways....
and D-mannosamine
Mannosamine
Mannosamine is a hexosamine derivative of mannose....
(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
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
s and ganglioside
Ganglioside
Ganglioside is a molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain. The 60+ known gangliosides differ mainly in the position and number of NANA residues.It is a component of the cell plasma membrane that modulates cell signal transduction events...
s. The N- or O-substituted derivatives of neuraminic acid are collectively known as sialic acid
Sialic acid
Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone. It is also the name for the most common member of this group, N-acetylneuraminic acid...
s, the predominant form in mammalian cells being N-acetylneuraminic acid
N-Acetylneuraminic acid
N-Acetylneuraminic acid is the predominant sialic acid found in mammalian cells.This negatively charged residue is found in complex glycans on mucins and glycoproteins found at the cell membrane...
. 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..
The symbol commonly 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. For example, N-acetyl-neuraminic acid, Neu5Ac, is typical in human glycoproteins.
Among their many biological functions, these structures are substrates for neuraminidase
Neuraminidase
Neuraminidase enzymes are glycoside hydrolase enzymes that cleave the glycosidic linkages of neuraminic acids. Neuraminidase enzymes are a large family, found in a range of organisms. The most commonly known neuraminidase is the viral neuraminidase, a drug target for the prevention of the spread...
enzymes which cleave neuraminic acid residues. Human flu viruses have a neuraminidase enzyme, signified in the name "H#N#", where the H refers to an isoform of hemaglutinin and N refers to an isoform of viral neuraminidase
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...
.