3-O-{beta-D-GlcA-(1->3)-[beta-D-GalNAc-(1->4)-beta-D-GlcA-(1->3)](n)-beta-D-GalNAc-(1->4)-beta-D-GlcA-(1->3)-beta-D-Gal-(1->3)-beta-D-Gal-(1->4)-beta-D-Xyl}-L-seryl-[protein] + UDP + H(+) => 3-O-{[beta-D-GalNAc-(1->4)-beta-D-GlcA-(1->3)](n)-beta-D-GalNAc-(1->4)-beta-D-GlcA-(1->3)-beta-D-Gal-(1->3)-beta-D-Gal-(1->4)-beta-D-Xyl}-L-seryl-[protein] + UDP-alpha-D-glucuronate
3-o-{beta-d-glca-(1->3)-[beta-d-galnac-(1->4)-beta-d-glca-(1->3)](n)-beta-d-galnac-(1->4)-beta-d-glca-(1->3)-beta-d-gal-(1->3)-beta-d-gal-(1->4)-beta-d-xyl}-l-seryl-[protein] + udp + h(+) => 3-o-{[beta-d-galnac-(1->4)-beta-d-glca-(1->3)](n)-beta-d-galnac-(1->4)-beta-d-glca-(1->3)-beta-d-gal-(1->3)-beta-d-gal-(1->4)-beta-d-xyl}-l-seryl-[protein] + udp-alpha-d-glucuronate