Antiporter that transports nucleotide sugars across the endoplasmic reticulum (ER) membrane in exchange for either their cognate nucleoside monophosphate or another nucleotide sugar (PubMed:16965264, PubMed:17599910, PubMed:31423530). Transports various UDP-sugars including UDP-N-acetyl-alpha-D-glucosamine (UDP-GlcNAc), UDP-N-acetyl-alpha-D-galactosamine (UDP-GalNAc) and UDP-alpha-D-glucuronate (UDP-GlcA), which are used by ER glucosyltransferases as sugar donors for the synthesis of sugar chains of glycoproteins, glycolipids and oligosaccharides (PubMed:11322953, PubMed:16965264, PubMed:17599910, PubMed:17952091, PubMed:31423530). May couple UDP-GlcNAc or UDP-GalNAc efflux to UDP-GlcA influx into the ER lumen that in turn stimulates glucuronidation and subsequent excretion of endobiotics and xenobiotics (PubMed:16965264, PubMed:17599910). Plays a role in chondroitin sulfate biosynthesis, which is important for formation of cartilage extracellular matrix and normal skeletal development (By similarity).
