Probable UDP-sugar:UMP transmembrane antiporter involved in UDP-alpha-D-glucuronate/UDP-GlcA, UDP-GlcNAc/UDP-N-acetyl-alpha-D- glucosamine and UDP-N-acetyl-alpha-D-galactosamine/UDP-GalNAc transport from the cytosol to the lumen of the Golgi. . This is the function of ENSG00000138459 (SLC35A5, solute carrier family 35 member A5).