Chondroitin synthase

Chondroitin synthase is an enzyme activity that builds the alternating glucuronic acid and N-acetylgalactosamine backbone of chondroitin using activated sugar donors. Making that backbone is distinct from adding the sulfate substitutions found in chondroitin sulfate.^[ref]

A particularly informative bacterial example was characterized from Pasteurella multocida type F. The tested soluble recombinant preparation contained residues 1–704 of a 965-residue protein. It extended chondroitin oligosaccharide acceptors using UDP-N-acetylgalactosamine and UDP-glucuronic acid, with both required transfer activities attributed to one polypeptide in this example.^[ref]

Product characterization went beyond observing expression of the cloned gene. Size-exclusion chromatography examined product size, while susceptibility to chondroitin AC lyase and resistance to hyaluronan lyase supplied complementary evidence about product identity. Related nucleotide-sugar donors did not simply substitute in the reported elongation assay.^[ref]

An invented counting example shows why incorporation and size are different measurements. Twenty chains each receiving fifty complete two-sugar repeats incorporate $20\times 50\times 2=2000$ sugar residues. Ten chains each receiving one hundred repeats also incorporate $10\times 100\times 2=2000$ residues. A bulk incorporation signal alone cannot distinguish those populations. Characterizing the size distribution answers an additional question about how the same total material is organized.