Terminology
Chondroitin sulfate was originally isolated well before the structure was characterised, leading to changes in terminology with time. Early researchers identified different fractions of the substance with letters.
| Letter identification | Site of sulfation | Systematic name |
| Chondroitin sulfate A | carbon 4 of the N-acetylgalactosamine (GalNAc) sugar | chondroitin-4-sulfate |
| Chondroitin sulfate C | carbon 6 of the GalNAc sugar | chondroitin-6-sulfate |
| Chondroitin sulfate D | carbon 2 of the glucuronic acid and 6 of the GalNAc sugar | chondroitin-2,6-sulfate |
| Chondroitin sulfate E | carbons 4 and 6 of the GalNAc sugar | chondroitin-4,6-sulfate |
"Chondroitin sulfate B" is an old name for dermatan sulfate, and it is no longer classified as a form of chondroitin sulfate.
Chondroitin, without the "sulfate", has been used to describe a fraction with little or no sulfation. However, this distinction is not used by all.
Although the name "chondroitin sulfate" suggests a salt with a sulfate counter-anion, this is not the case, as sulfate is covalently bonded to the sugar. Rather, since the molecule has multiple negative charges at physiological pH, a cation is present in salts of chondroitin sulfate. Commercial preparations of chondroitin sulfate typically are the sodium salt. Barnhill et al. have suggested that all such preparations of chondroitin sulfate be referred to as "sodium chondroitin" regardless of their sulfation status.
Read more about this topic: Chondroitin Sulfate