Nucleotide sugars are used as sugar donors by glycosyltransferases to create the sugar chains for glycoconjugates such as glycoproteins, polysaccharides and glycolipids. Glycosyltransferases reside mainly in the lumen of the Golgi apparatus and endoplasmic reticulum (ER) whereas nucleotide sugars are synthesized in the cytosol. The human solute carrier family SLC35 encode nucleotide sugar transporters (NSTs) which can mediate the antiport of nucleotide sugars in exchange for the corresponding nucleoside monophosphates (eg. UMP for UDP-sugars). Owing to their function, NSTs are primarily located on Golgi and ER membranes (He L et al, 2009; Handford M et al, 2006; Ishida N and Kawakita M, 2004).