3-O-(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)-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)-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)-beta-d-gal-(1->3)-beta-d-gal-(1->4)-beta-d-xyl)-l-seryl-[protein] + udp + h(+)