L. Puglielli et al., Identification and purification of the rat liver Golgi membrane UDP-N-acetylgalactosamine transporter, J BIOL CHEM, 274(7), 1999, pp. 4474-4479
Glycosylation of glycoproteins, proteoglycans, and glycosphingolipids occur
s mainly in the lumen of the endoplasmic reticulum and the Golgi apparatus.
Nucleotide sugars, donors of all the sugars involved in Gels glycosylation
reactions, are synthesized in the cytoplasm and require specialized transp
orters to be translocated into the lumen of the Golgi apparatus. By control
ling the supply of sugar nucleotides in the lumen of the Golgi apparatus, t
hese transporters directly regulate the glycosylation of macromolecules tra
nsiting the Golgi, We have identified and purified the rat liver Golgi memb
rane UDP-N-acetylgalactosamine transporter. The transporter was purified to
apparent homogeneity by a combination of conventional and dye color chroma
tography, An similar to 63,000-fold purification (6% yield) was achieved st
arting from crude rat liver Golgi membranes and resulting in a protein with
an apparent molecular mass of 43 kDa, The transporter was active when reco
nstituted into phosphatidylcholine vesicles and could be specifically photo
labeled with P-3-(4-azidoanilido)-uridine-5'-[p(1)-P-32]triphosphate, an an
alog of UDP-N-acetylgalactosamine. Native functional size determination on
a glycerol gradient suggested that the transporter exists as a homodimer wi
thin the Golgi membrane.