= Chondroitin 6-sulfate
<Chondroitin 6-sulfate> is a positional form of <chondroitin sulfate> characterized by sulfate substitution at the 6-position of <N-acetylgalactosamine> residues. The numeral identifies a position within a sugar residue; it does not mean that a chain contains exactly six sulfate groups. The alternating <chondroitin> backbone still contains <glucuronic acid> and <N-acetylgalactosamine>-derived residues.
The position can be specified through a defined reaction. <Chondroitin 6-sulfotransferase> transfers a group from <PAPS> to the 6-position of eligible <N-acetylgalactosamine> in <chondroitin>. Its activity is distinct from that of <chondroitin 4-sulfotransferase>, which targets a different position.<Chondroitin 6-sulfotransferase in IUBMB Enzyme Nomenclature>[EC2.8.2.17: Reaction and Comments, 6-position and distinction from EC2.8.2.5]{ref}
For an original ideal segment, take ten complete two-sugar repeats and suppose every one of its ten eligible amino-sugar residues carries one 6-position substitution. The segment then contains 20 sugar residues and ten sulfate substitutions. Partial modification would change the substitution count without changing the number of backbone residues.
<Chondroitin 6-sulfate> and <chondroitin 4-sulfate> can consequently share sugar and sulfate counts while differing in local chemical structure. A total sulfur assay alone cannot identify which positions are modified. Comparing preparations requires stating the structural feature measured, rather than assigning every chain one uniform substitution pattern.<Chondroitin sulfate in ChEBI>[CHEBI:37397, separately classified 4- and 6-sulfated forms]{ref}
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