Fig. 4.

Overview of pathways for pentose utilization covered by patent applications of DSM and Royal Nedalco. d-xylose and l-arabinose can be utilized by two pathways: (1) aldose reductase NADPH-dependent and (2) isomerase cofactors-independent. In case of the latter, requirement of cofactor balance is eliminated and enhancing activity of isomerase remains main issue. Two Dutch companies, DSM and Royal Nedalco, claim over-expression of heterologous xylose isomerases from Thermotoga maritime MSB8 and Piromyces sp. E2 (ATCC 76762), respectively. Xylulokinase and enzymes in pentose phosphate pathway were also amplified simultaneously. Arabinose genes in isomerase pathway such as l-arabinose isomerase, l-ribulokinase, and l-ribulose-5P 4-epimerase originated from Lactobacillus plantarum in DSM and Arthrobacter aurescens, Clavibacter michiganensis, Gramella forsetii in Royal Nedalco were amplified with enzymes in pentose phosphate pathways