Simultaneous sulfation of endogenous chondroitin sulfate and chondroitin-derived oligosaccharides. Studies with separate 4-sulfating and 6-sulfating microsomal systems.

Microsomal preparations from chondroitin 6-sulfate-producing chick embryo epiphyseal cartilage and from chondroitin 4-sulfate-producing mouse mastocytoma cells were incubated with varying concentrations of 3'-phosphoadenylylphospho[35S]sulfate and chondroitin hexasaccharide in the presence or absence of Triton X-100. [35S]Sulfate incorporation into hexasaccharide and into endogenous microsomal chondroitin 6-sulfate or endogenous microsomal chondroitin 4-sulfate was measured. With both microsomal systems, Triton X-100 increased the incorporation of [35S]sulfate into hexasaccharide but had much less effect on the incorporation into endogenous chondroitin sulfate. Higher concentrations of hexasaccharide inhibited the incorporation of [35S]sulfate into endogenous chondroitin sulfate. The apparent Km for 3'-phosphoadenylylphosphosulfate for both the 6-sulfotransferase and 4-sulfotransferase with hexasaccharide and with endogenous chondroitin sulfate in the presence or absence of Triton X-100 were all similar. However, the apparent Km for hexasaccharide was lower in the presence of Triton X-100 for both the microsomal sulfotransferases. This is consistent with solubilization of sulfotransferases, and indicates that hexasaccharide access to these enzymes had been limited in the particulate system. Examination of 35S-oligosaccharide products formed with each system demonstrated good 6-sulfation or 4-sulfation of penultimate GalNAc at the non-reducing end of the chondroitin hexasaccharide. However, no 6-sulfation of terminal GalNAc at the non-reducing end of a chondroitin pentasaccharide derived from hexasaccharide was observed, and there was only minimal 4-sulfation of this terminal GalNAc. Concurrent addition of GalNAc to hexasaccharide resulting in heptasaccharide did not appear to promote significant 6-sulfation or 4-sulfation of newly added non-reducing terminal GalNAc.