effects of growth factors by a shield of hyaluronan and minimally sulfated chondroitin sulfate. During progenitor division, the daughter cell moves outside of this pericellular shield where it can then be influenced by growth factors to differentiate even further. Classification Members of the glycosaminoglycan family vary in the type of hexosamine, hexose or hexuronic acid unit they contain (e.g. glucuronic acid, iduronic acid, galactose, galactosamine, glucosamine). They also vary in the geometry of the glycosidic linkage. Examples of GAGs include: {| class="wikitable" ! Name || Hexuronic acid orhexose (for keratan) || Hexosamine || Linkage geometry between predominant monomeric units || Unique features |- |-valign="top" | Chondroitin sulfate || GlcUA orGlcUA(2S) || GalNAc orGalNAc(4S) orGalNAc(6S) orGalNAc(4S,6S) || GlcUAβ(1→3)GalNAcβ(1→4) || Most prevalent GAG |- |-valign="top" | Dermatan sulfate || GlcUA orIdoUA orIdoUA(2S) || GalNAc orGalNAc(4S) orGalNAc(6S) orGalNAc(4S,6S) || 'IdoUAβ1-3GalNAcβ1-4 || Distinguished from chondroitin sulfate by the presence of iduronic acid, although some hexuronic acid monosaccharides may be glucuronic acid. |- |-valign="top" | Keratan sulfate || Gal orGal(6S) || GlcNAc orGlcNAc(6S) || -Gal(6S)β1-4GlcNAc(6S)β1-3 || Keratan sulfate type II may be fucosylated. |- |-valign="top" | Heparin || GlcUA orIdoUA(2S) || GlcNAc orGlcNS orGlcNAc(6S) orGlcNS(6S) || -IdoUA(2S)α1-4GlcNS(6S)α1-4 || Highest negative charge density of any known biological molecule |- |-valign="top" | Heparan sulfate || GlcUA orIdoUA orIdoUA(2S) || GlcNAc orGlcNS orGlcNAc(6S) orGlcNS(6S) || -GlcUAβ1-4GlcNAcα1-4 || Highly similar in structure to heparin, however heparan sulfate's disaccharide units are organised into distinct sulfated and non-sulfated domains. |- |-valign="top" | Hyaluronan || GlcUA || GlcNAc || -GlcUAβ1-3GlcNAcβ1-4 || The only GAG that is exclusively non-sulfated |} Abbreviations GlcUA = β-D-glucuronic acid GlcUA(2S) = 2-O-sulfo-β-D-glucuronic acid IdoUA = α-L-iduronic acid IdoUA(2S) = 2-O-sulfo-α-L-iduronic acid Gal = β-D-galactose Gal(6S) = 6-O-sulfo-β-D-galactose GalNAc = β-D-N-acetylgalactosamine GalNAc(4S) = β-D-N-acetylgalactosamine-4-O-sulfate GalNAc(6S) = β-D-N-acetylgalactosamine-6-O-sulfate GalNAc(4S,6S) = β-D-N-acetylgalactosamine-4-O, 6-O-sulfate GlcNAc = α-D-N-acetylglucosamine GlcNS = α-D-N-sulfoglucosamine GlcNS(6S)''' = α''-D-N-sulfoglucosamine-6-O-sulfate See also Lipopolysaccharide References External links King M. 2005. Glycosaminoglycans. Indiana University School of Medicine Accessed December 31, 2006. MRI evaluation of glycosaminoglycan loss (dGEMRIC evaluation)