Converts D-glucuronic acid to L-iduronic acid (IdoUA) residues. Plays an important role in the biosynthesis of the glycosaminoglycan/mucopolysaccharide dermatan sulfate. chondroitin 4'-sulfate = dermatan 4'-sulfate Also has weak activity in the presence of Mg(2+) or Ca(2+) ions. Optimum pH is 5.5. Glycan metabolism; chondroitin sulfate biosynthesis. Glycan metabolism; heparan sulfate biosynthesis. Ubiquitously expressed with higher expression in kidney and ovary and lower expression in brain, colon and thymus. Also expressed in renal cell carcinomas, brain tumors, and in a part of melanomas and adenocarcinomas from organs other than the breast. Expressed in squamous cell carcinomas (SCC), glioma, and some adenocarcinoma cell lines, but not in breast cancer cell lines or any normal tissues (at protein level). N-glycosylated (PubMed:19004833, Ref.7). Glycosylation is important for enzymatic activity (PubMed:19004833). The disease is caused by variants affecting the gene represented in this entry. Belongs to the dermatan-sulfate isomerase family.