title: Evidence for a UDP-Glucose Transporter in Golgi Apparatus-Derived Vesicles from Pea and Its Possible Role in Polysaccharide Biosynthesis.
abstract: The Golgi apparatus in plant cells is involved in hemicellulose and pectin biosynthesis. While it is known that glucan synthase I is responsible for the formation of [beta]-l-4-linked glucose (Glc) polymers and uses UDP-Glc as a substrate, very little is known about the topography of reactions leading to the biosynthesis of polysaccharides in this organelle. We isolated from pea (Pisum sativum) stems a fraction highly enriched in Golgi apparatus-derived vesicles that are sealed and have the same topographical orientation that the membranes have in vivo. Using these vesicles and UDP-Glc, we reconstituted polysaccharide biosynthesis in vitro and found evidence for a luminal location of the active site of glucan synthase I. In addition, we identified a UDP-Glc transport activity, which is likely to be involved in supplying substrate for glucan synthase I. We found that UDP-Glc transport is protein mediated. Moreover, our results suggest that UDP-Glc transport is coupled to the exit of a luminal uridine-containing nucleotide via an antiporter mechanism. We suggest that UDP-Glc is transported into the lumen of Golgi and that Glc is transferred to a polysaccharide chain, whereas the nucleotide moiety leaves the vesicle by an antiporter mechanism.
authors.affiliation: Department of Biology, Faculty of Sciences, University of Chile, Casilla 653, Santiago, Chile.
authors.forename: P.
authors.initials: P
authors.lastname: Munoz
authors.forename: L.
authors.initials: L
authors.lastname: Norambuena
authors.forename: A.
authors.initials: A
authors.lastname: Orellana