A distinct terminal structure in newly synthesized chondroitin sulphate chains

A method was developed for the analysis of non-reducing terminal structure of radiolabelled chondroitin sulphate chains with the aid of N-acetylgalactosamine 4-sulphatase ('terminal 4-sulphatase'), N-acetylgalactosamine 6-sulphatase ('terminal 6-sulphatase'), beta-glucuronidase and beta-N-acetylhexosaminidase. Studies with this method on the non-reducing terminal structure of [35S]sulphate- and [3H]glucose-labelled chondroitin sulphate chains from rat and chick-embryo cartilages showed that the presence of a high proportion of 4-sulphated hexosamine residues is a common feature of the termini of newly synthesized chondroitin sulphate chains. Of the non-reducing terminal 4-sulphated hexosamine residues, about 14% (chick embryo) or 46% (rat) contained an additional sulphate group at position 6. The internal portion of the chondroitin sulphate chains, in contrast, contained little or no 4,6-bis-sulphated hexosamine residue, suggesting that 4,6-bis-sulphated structure may play a role in biosynthetic control at the level of chain termination.