Fig. 1

Simplified bacterial (left) and fungal (right) l-arabinose degradation pathway used for metabolic engineering of S. cerevisiae. l-Arabinose is taken up via Gal2p in both pathways. The further l-arabinose catabolism is linked to the central carbon metabolism via d-xylulose-5-P, an intermediate of the pentose phosphate pathway. In the fungal route, l-arabinose is reduced to l-arabinitol by the xylose reductase Xyl1p and further oxidized to l-xylulose catalyzed by the l-arabinitol 4-dehydrogenase Lad1p. l-Xylulose is then reduced to xylitol by the l-xylulose reductase Xyl2p, which is further oxidized to d-xylulose by the xylitol dehydrogenase Xyl2p. The conversion of d-xylulose to d-xylulose-5-P by the xylulokinase Xks1p is the final step. In the bacterial route, l-arabinose is converted to l-ribulose by the isomerase AraA, phosphorylated to l-ribulose-5-P via the l-ribulokinase AraB and converted to d-xylulose-5-P by the l-ribulose-5-P 4-epimerase AraD. All steps of the bacterial route are cofactor-independent