Sialic acid
From Wikipedia, the free encyclopedia
Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. Sialic acids are found widely distributed in animal tissues and in bacteria, especially in glycoproteins and gangliosides. 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.
Sialic acid rich glycoproteins bind selectin in humans and other organisms. Cancer cells that can metastasize often have a lot of sialic acid rich glycoproteins. This helps these late stage cancer cells enter the blood stream.
Sialic acid-rich oligosaccharides on the surface membrane glycoconjugates help keep water at the surface of cells. The sialic acid-rich regions contribute to creating a negative charge on the cells surface. Since water is a polar molecule, it has a partial positive charge on both hydrogen molecules, it is attracted to cell surfaces and membranes. This also contribues to cellular fluid uptake.
The term "sialic acid" (from the Greek σιαλοσ (sialos) 'saliva') was first introduced by Swedish biochemist, Gunnar Blix, in 1952.
[edit] N-acetylneuraminic acid
The predominant sialic acid is N-acetylneuraminic acid (Neu5Ac), aka NANA. The negative charge of this chemical is responsible for the slippery feel of saliva and mucins coating the body’s organs. Despite its role of acting as "decoy" for invading pathogens, Neu5Ac is becoming known as an agent necessary for mediating ganglioside distribution and structures in the brain. Along with involvement in preventing infections (mucous associated with mucous membranes - mouth, nose, GI, respiratory tract), Neu5Ac acts as a receptor for influenza viruses to allow attachment to mucous cells (an early step in contracting the flu).
