Glycosaminoglycan Biosynthesis in Arterial Wall

Incubation of microsomal fractions with labelled 3′‐phosphoadenylyl sulfate results in incorporation of [ 35 S]sulfate into endogenous glycosaminoglycans. Specific radioactivity observed incorporated into heparan sulfate chains is 10‐fold greater than that incorporated into chondroitin sulfate chains. This is in agreement with the results obtained for glycosylation of glycosaminoglycans in arterial wall membrane fractions. Sulfation of heparan sulfate was studied since it contains N ‐ and O ‐sulfate groups in contrast with the other sulfated glycosaminoglycans which contain only O ‐sulfate groups. Sulfation of heparan sulfate occurs rapidly, since sulfate incorporation is detected after exposure for only 0.5 min. Heparan sulfate was identified on the basis of its resistance to hyaluronidase and chondroitin ABC lyase, its susceptibility to heparitinase, its sensitivity to nitrous acid and the presence of glucosamine as the only hexosamine. The chemical composition of the purified heparan sulfate fractions provides evidence for the high degree of sulfation of its chains. Studies into the distribution of sulfate residues on heparan sulfate at different times of sulfation indicate that N ‐sulfate groups are not randomly introduced into the polymer. The relationship between the processes of N ‐ and O ‐sulfation was studied. The present results demonstrate that preferential N ‐sulfation is obtained for incorporation of labelled precursor over a short period, the O ‐sulfation occurring on previously N ‐sulfated heparan sulfate.