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The metabolic response of lactose-assimilating yeasts to changes of cultivation conditions after addition of furfural into the medium was explored. Two yeast strains were studied— Candida blankii 35 with an oxidative metabolism, and C. pseudotropicalis 11 with a fermentative metabolism. Strains were cultivated in a chemostat under carbon limitation and dilution rates D = 0.1 and 0.25 h −1 . During the transition period after a shock treatment with 0.04% furfural, changes of the following enzymes of the carbon metabolism were studied: hexokinase (HK), glucosephosphate isomerase (GPI) and glyceraldehyde-3P-dehydrogenase (GAPD) of the glycolysis, glucose-6P-dehydrogenase (GPD) from the pentosophosphate cycle, as well as β-galactosidase. Results show that during cultivation of C. pseudotropicalis 11 at D = 0.1 h −1 , furfural concentration of 0.04% caused increase of the glycolytic enzyme activities, while the level of GPD activity remained rather constant. At the higher dilution rate D = 0.25 h −1 the effect of furfural brought to a significant decrease of all enzyme activities studied, except β-galactosidase, for which activity registered at both dilution rates was significantly higher. During cultivation of C. blankii 35 at D = 0.1 h −1 , furfural brought to lower activities of GPI and GPD, while HK activity was not affected by the inhibitor, and that of GAPD increased. The furfural shock at D = 0.25 h −1 leads to increased activity of the three glycolytic enzymes, while that of GPD was 33.6% lower as compared to control. Addition of furfural into the cultivation medium of the oxidative strain caused decrease of β-galactosidase activity. |
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