= 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>.<Identification and molecular cloning of a chondroitin synthase from Pasteurella multocida type F by P. L. DeAngelis and A. J. Padgett-McCue>[Abstract, product composition and donor-dependent chain extension]{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.<Identification and molecular cloning of a chondroitin synthase from Pasteurella multocida type F by P. L. DeAngelis and A. J. Padgett-McCue>[Abstract, truncated soluble construct and repetitive transfer from the two donors]{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.<Identification and molecular cloning of a chondroitin synthase from Pasteurella multocida type F by P. L. DeAngelis and A. J. Padgett-McCue>[Abstract, donor specificity, size analysis and contrasting lyase susceptibility]{ref}
An invented counting example shows why incorporation and size are different measurements. Twenty chains each receiving fifty complete two-sugar repeats incorporate $20\times50\times2=2000$ sugar residues. Ten chains each receiving one hundred repeats also incorporate $10\times100\times2=2000$ 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.
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