Study of transhydrogenase systems features in the mutants of the yeast pachysolen tannophilus for the production of ethanol and xylitol from agricultural wastes
The key catabolic enzymes of D-xylose, an important structural component of different
agricultural wastes, were studied in cells of mutant strains of the xylose-assimilating yeast
Pachysolen tannophilus. The evaluation of catalytic activity and cofactor specificity of xylose
reductase (ЕС 1.1.1.307) and xylitol dehydrogenase (ЕС 1.1.1.9) confirmed the dependence of
intracellular catabolic pathway for D-xy lose on the NAD×H/NADP×H ratio, formed under
microaerobic conditions. The study of total activity of some NAD+
/NAP×H-dependent
dehydrogenases revealed the metabolic characteristics of the yeast cells, which could ensure
selective ethanol or xylitol production. Thus, the efficient involvement of D-xylose into the
Embden–Meyerhof–Parnas pathway provided not only the high activities of xylose reductase and
xylitol dehydrogenase, but also of 1-glycerophosphate dehydrogenase (EC 1.1.1.8) and lactate
dehydrogenase (ЕС 1.1.1.27), respectively. The inhibition of activity of these enzymes led to
selective production of xylitol from D-xylose. On the base of the experimental results, the
principles of metabolic engineering of xylose-assimilating yeasts were formulated. The
possibility of bioethanol and xylitol production from different agricultural wastes using xyloseassimilating yeasts are discussed