The function of ENSG00000138604 (GLCE, glucuronic acid epimerase) is as follows. Converts D-glucuronic acid residues adjacent to N-sulfate sugar residues to L-iduronic acid residues, both in maturing heparan sulfate (HS) and heparin chains. This is important for further modifications that determine the specificity of interactions between these glycosaminoglycans and proteins. {ECO:0000269|PubMed:20118238, ECO:0000269|PubMed:22528493, ECO:0000269|PubMed:30872481}.