UDP-arabinose

The wheat germ enzyme was purified 350-foId by Ankel and Feingold (1965) and the purified enzyme was found to contain approximately 1 mole of NAD per 600,000 gm of protein. The nucleotide was tightly bound and could not be removed by charcoal treatment or by digestion with NADase (E.C.3.2.2.5). The enj me has a Km of 3 X 10 M and a pH optimum of 6.8-7.0. It is inhibited by UMP, UDP, UDP-glucose, UDP-arabinose, and UDP-xylose, the most effective being UDP and UDP-xylose, which inhibited 60% and 20% respectively, at a concentration one-tenth that of the substrate. 

Particulate preparations from com shoots readily incorporate 14C-labeled D-xylose from UDP-D-xylose-14C into a polysaccharide in which the D-xylose residues are combined by / -l,4-D-xylosyl bonds (31). It was shown that this polysaccharide, similar to natural plant xylan, contains a small proportion of L-arabinose units which have the furanose configuration. 

Breazeale, S.D., Ribeiro, A.A., McClerren, A.L., Raetz, C.R.H. A formyltransferase required for polymyxin resistance in Escherichia coli and the modification of lipid A with 4-amino-4-deoxy-L-arabinose. Identification and function of UDP-4-deoxy-4-formamido-L-arabinose. J Biol Chem 280 (2005) 14154-14167. 

Burget, E.G., Verma, R., Molho, M., and Reiter, W.-D., 2003, The biosynthesis of L-arabinose in plants Molecular cloning and characterization of a Golgi-localized UDP-D-xylose 4-epimerase encoded by the MUR4 gene of Arabidopsis. Plant Cell 15 523-531. 

In comparison with mammals, plants contain considerably more GTs because, in addition to the reactions carried out by mammalian GTs, they are required to convert the products of photosynthesis into diverse cell carbohydrates. For example, these GTs synthesize cell wall polysaccharides as well as secondary metabolites and xenobiotics. Plant GTs differ from mammalian GTs even more by their diversity of nucleotide donors. They use not only eight of the nine mammalian nucleotide donors, but numerous others such as UDP-L-rhamnose, GDP-L-glucose, GDP-L-galactose, UDP-L-arabinose, UDP-D-galacturonic acid, UDP-D-apiose, and so on. (29). 

Klaflfke developed a scaleable three step synthetic method to prepare uridine diphospho-D-xylose and UDP-L-arabinose from D-xylal and L-arabinal respectively and The synthesis of ADP- h-glycero- and T>-glycero-... 

Pathways in the formation of NDP-sugars. A seiection of monosaccharide conversions occurring at the phosphate ester and nucieotide-monosaccharide ievei in animais, piants and bacteria are shown all pathways radiate from fructose-6-phosphate, indicating the central role of this metabolite. The dTDP, GDP and UDP-yV-acetylmu-ramic pathways are peculiar to bacteria, whereas ADP-o-glucose, UDP-o-apiose and UDP-L-arabinose are found in plants. For reasons of simplicity, other pathways, e. g., to UDP-L-rhamnose in plants, GDP-o-rhamnose in Pseudomonas aeroginosa and GDP-o-arabinose in trypanosomatids are not included. The figure is reproduced from Chap. 6.4 of the first edition of this book... 

Little is known about the L-arabinofuranosyl transfer machinery. A gene in the genome of A. thaliana has been identified as a membrane-bound arabino-furanosyl transferase by its membrane-insertion sequence and the fact that mutants in the gene led to expression of mRNA, but phenotypes that were nonetheless defective in arabinan side-chains of their pectin. Attempts to use UDP-a-L-arabinopyranose as arabinofuranose donor in crude extracts, presumably in an attempt to uncover any mutase similar to UDP galactopyranose mutase (see Section 5.12.4), merely resulted in the incorporation of pyranose units into the arabinan. However, an enzyme using this donor has been shown to add the terminal arabinopyranosyl residue to the 3-position of the terminal arabinose of the 1,5-arabininan of rhamnogalacturonan 1. [By contrast, the o-arabinofuranosyl transfer machinery that produces the... 

---