FIGURE 2.

The proposed non-phosphorylative Entner-Doudoroff pathway for the catabolism of d-xylose and l-arabinose in S. solfataricus. The scheme proposed in this paper is shown in solid arrows. The xylose dehydrogenase is the same protein as that labeled glucose dehydrogenase in Fig. 1, the one enzyme being catalytically active with d-glucose, d-galactose, d-xylose, and l-arabinose. The KDG-aldolase is proposed to catalyze the aldol cleavage of KD-gluconate and KD-galactonate (see Fig. 1) and of KD-xylonate and KD-arabinonate. The direct conversion of KD-xylonate to 2-oxoglutarate, as proposed by Brouns et al. (8), is shown with dotted arrows. DOP dehydrogenase, 2,5-dioxopentanoate dehydrogenase.