SUMMARY: A mutant of unable to grow on -xylose and -arabinose has been isolated. Genetic analysis revealed that the mutation is located on linkage group IV. Enzymic analysis revealed a deficiency in -xylulose kinase activity. After transfer of growing mycelium to a medium containing either -xylose or -arabinose, the mutant accumulates large amounts of arabitol and xylitol, as shown by 1C NMR spectroscopy. These data and an analysis of enzyme activities induced by -xylose and -arabinose in the wild-type strain led to the following catabolic pathway for -xylose: -xylose - xylitol - -xylulose - -xylulose 5-phosphate; and for -arabinose: -arabinose - -arabitol - -xylulose - xylitol - -xylulose - -xylulose 5-phosphate. The reduction steps of the sugars to the corresponding polyols are all NADPH dependent. The oxidation steps of the polyols to the sugars are all NAD dependent. Fractionation of cell-free extracts gave information about the specificity of the enzymes and showed that all the reactions are catalysed by different enzymes.


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