Abstract
UDP-sugars, activated forms of monosaccharides, are synthesized through de novo and salvage pathways and serve as substrates for the synthesis of polysaccharides, glycolipids, and glycoproteins in higher plants. A UDP-sugar pyrophosphorylase, designated PsUSP, was purified about 1,200-fold from pea sprouts by conventional chromatography. The enzyme catalyzed the formation of UDP-Glc, UDP-Gal, UDP-glucuronic acid, UDP-L-arabinose, and UDP-xylose from respective monosaccharide 1-phosphates in the presence of UTP as a co-substrate, indicating that the enzyme has broad substrate specificity toward monosaccharide 1-phosphates. PsUSP cDNA was cloned by reverse transcriptase-PCR. Phylogenetic analysis revealed that PsUSP can be categorized in a group together with homologues from Arabidopsis and rice, which is distinct from the UDP-Glc and UDP-N-acetylhexosamine pyrophosphorylase groups. These results indicate that the enzyme is a novel type of UDP-sugar pyrophosphorylase, which catalyzes the formation of various UDP-sugars at the end of salvage pathways in higher plants.
