Study of transhydrogenase systems features in the mutants of the yeast pachysolen tannophilus for the production of ethanol and xylitol from agricultural wastes
¹Petrozavodsk State University, Institute of Medicine, Department of
biomedical chemistry, immunology and laboratory diagnostics, Lenina Str., 33,
RU 185910 Petrozavodsk, Republic of Karelia, Russia
²Peter the Great St. Petersburg Polytechnic University, Graduate school of biotechnology and food science, Polytechnicheskaya Srt., 29, RU 195251 Saint Petersburg, Russia
Abstract:
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.
Key words:
1-glycerophosphate dehydrogenase, agricultural wastes, D-xylose, ethanol, lactate dehydrogenase, mutants of the yeast P. tannophilus, xylitol, xylitol dehydrogenase, xylose reductase