L-Arabinose and D-Xylose Catabolism in Aspergillus niger

Abstract

SUMMARY: A mutant of Aspergillus niger unable to grow on D-xylose and L-arabinose has been isolated. Genetic analysis revealed that the mutation is located on linkage group IV. Enzymic analysis revealed a deficiency in D-xylulose kinase activity. After transfer of growing mycelium to a medium containing either D-xylose or L-arabinose, the mutant accumulates large amounts of arabitol and xylitol, as shown by 13C NMR spectroscopy. These data and an analysis of enzyme activities induced by D-xylose and L-arabinose in the wild-type strain led to the following catabolic pathway for D-xylose: D-xylose - xylitol - D-xylulose - D-xylulose 5-phosphate; and for L-arabinose: L-arabinose - L-arabitol - L-xylulose - xylitol - D-xylulose - D-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.