L-Arabinitol 4-dehydrogenase (Lad1) of the cellulolytic and hemicellulolytic fungusHypocrea jecorina(anamorph: Trichoderma reesei) has been implicated in the catabolism ofL-arabinose, and genetic evidence also shows that it is involved in the catabolism of D-xylose in xylitol dehydrogenase (xdh1) mutants and of D-galactose in galactokinase (gal1) mutants of H. order to identify the substrate specificity of Lad1, we have recombinantly produced the enzyme inEscherichia coliand purified it to physical homogeneity