Converts D-glucuronic acid residues adjacent to N-sulfate sugar residues to L-iduronic acids (By similarity). Plays a role in the early migration of AQR and PQR neurons, which descend from the Q neuroblasts (PubMed:26022293). [heparosan-N-sulfate](n) = [heparan-N-sulfate](n) Glycan metabolism; heparan sulfate biosynthesis. Glycan metabolism; heparin biosynthesis. Homodimer. Expression in comma stage embryos is strong in the hypodermis and intestine and weaker in the head region. In late embryos, larval, and adult stages, expressed primarily in hypodermis and intestine. Irregular positioning of the AQR and PQR neurons in larva at the L4 stage. Belongs to the D-glucuronyl C5-epimerase family.