L-Arabinose and D-Xylose Catabolism in Aspergillus niger

Abstract

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 I3C 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-xylosexylitol -D-xylulose -D-xylulose 5-phosphate; and for L-arabinose : L-arabinose -L-arabitol -L-xylulosexylitol -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. I N T R O D U C T I O N