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Partial Purification & Properties of Xylose & Ribose Isomerase in Higher Plants

1963; Oxford University Press; Volume: 38; Issue: 4 Linguagem: Inglês

10.1104/pp.38.4.457

1532-2548

M. H. Pubols, James C. Zahnley, Bernard Axelrod,

Pancreatic function and diabetes

The conversion of L-arabinose into the pentose moieties of plant polysaccharides proceeds wvith lit- tle rearrangement of the carbon skeleton (14,18).On the other hand D-ribose and D-xylose suffer con- siderable rearrangement.Experiments with specifically labeled sugars suggest that these twvo pentoses must pass through a hexose and indeed through the pentose phosphate pathway (1,3,8,10,14,17,18).The discovery by Hassid and his co-workers of L- arabinose kinase and the appropriate pyrophosphorylases and sugar nucleotide epimerases readily ac- counts for the observations with L-arabinose (19).However kinases for D-ribose and D-xylose have not been found in higher plants.A previous communication from this laboratory noted the presence in plant tissues of an enzyme, xylose isomerase which catalyzed the interconversion of D-xylose and D-xylulose (20).The action of a suitable kinase (for which we have presented in- direct evidence & which is currently the object of study in our laboratory) could yield D-xylulose-5phosphate which would serve to introduce the xylulose into the metabolic stream of the plant via the pentose phosphate pathway.It is the purpose of this paper to describe a partial purification of xylose isomerase from wheat germ, ancl to note some of its properties, including its ability to catalyze the interconversion of D-ribose and D-ribulose.The demonstration of xylose iso- merase activities in several other plant species point to a possibly general significance of this enzyme. Materials & MethodsReagents.All materials wvere obtained from commercial sources except as note-l.D-xylothiapyranose and 5-deoxy-5-thiobenzyl-D-xylose vere gifts of Drs.R. L.