= Chondroitin sulfate
<Chondroitin sulfate> is a class of sulfated <glycosaminoglycan> chains based on the alternating <glucuronic acid> and <N-acetylgalactosamine> framework of <chondroitin>. Chain length and substitution can vary; the name does not denote one small molecule with a unique <molecular formula>. A <proteoglycan> can contain a <chondroitin sulfate> chain as one component, while also including a protein core.<Chondroitin sulfate in ChEBI>[CHEBI:37397: sulfated glycosaminoglycan classification, functional parent and proteoglycan has-part relation]{ref}
Position matters as well as total sulfate content. <Chondroitin 4-sulfotransferase> uses <PAPS> to modify the 4-position of <N-acetylgalactosamine> residues, whereas <chondroitin 6-sulfotransferase> modifies the 6-position. These are distinct <enzyme> activities acting on a related backbone.<Chondroitin 4-sulfotransferase in IUBMB Enzyme Nomenclature>[EC2.8.2.5, Reaction and Comments]{ref}<Chondroitin 6-sulfotransferase in IUBMB Enzyme Nomenclature>[EC2.8.2.17, Reaction and Comments]{ref}
For an original structural-accounting example, take two segments that each contain ten complete repeats, hence 20 sugar residues. Give each segment six sulfate substitutions. In one, place all six at eligible 4-positions; in the other, place three at 4-positions and three at 6-positions. The segments share a sugar count and sulfate count but have different local chemical arrangements. A bulk sulfur measurement cannot distinguish these patterns by itself.
<Carbohydrate sulfation> and chain extension are thus different operations. Establishing the identity of a preparation can require information about backbone composition, length and substitution positions, rather than relying only on its negative charge or total carbohydrate content.
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