Host: The Japanese Society of Plant Physiologists
Pages 0272
Interconversion between UDP-xylose (UDP-Xyl) and UDP-L-arabinose (UDP-L-Ara) is catalyzed by a membrane-anchored UDP-Xyl 4-epimerase in the Golgi apparatus and essential for the syntheisis of L-Ara-containing cell wall polysaccharides in higher plans. In this study, a soluble UDP-Xyl 4-epimerase distinct from the enzyme in the Golgi apparatus was isolated from pea (Pisum sativum L.) sprouts and characterized. The N-terminal amino acid sequence revealed that the enzyme is encoded by a UDP-glucose (UDP-Glc) 4-epimerase gene, PsGalE. Recombinant PsGalE (rPsGalE) expressed in Escherichia coli showed both UDP-Xyl 4-epimerase and UDP-Glc 4-epimerase activities, confirming that PsGalE is a UDP-Glc 4-epimerase with broad substrate specificity toward UDP-sugars. The apparent Km values of rPsGalE for UDP-Glc UDP-galactose, UDP-Xyl, and UDP-L-Ara were 0.21 mM, 0.21 mM, 0.17 mM, and 0.14 mM, respectively. The results suggest that the interconversion between UDP-Xyl and UDP-L-Ara in cytoplasm is catalyzed by UDP-Glc 4-epimerase isoforms homologous to PsGalE in higher plants.
