Effect of furfural on nitrogen assimilating enzymes of the lactose utilizing yeasts Candida blankii 35 and Candida pseudotropicalis 11

The research was performed with two lactose-assimilating yeast strains—Candida blankii 35 with an oxidative metabolism and Candida pseudotropicalis 11 with a fermentative metabolism. The strains were cultivated in a chemostat under carbon limitation at dilution rates D = 0.1 and 0.25 h−1. After shock with 0.04% furfural, the changes of the following nitrogen enzyme activities were studied: NADPH-dependant glutamate dehydrogenase (NADPH-GDH), NADH-dependant glutamate dehydrogenase (NADH-GDH), glutamine synthetase (GS), glutamate synthase (GOGAT) and alanine dehydrogenase (ADH). Results show that during cultivation of C. blankii 35 at D = 0.1 h−1, furfural exhibits a clear inhibitory effect on the glutamate dehydrogenase and the alanine metabolite routes of ammonia ion assimilation. Furfural slows down the nitrogen assimilation of the strain through glutamate dehydrogenase and at D = 0.1 h−1 the GS/GOGAT system is activated. During the growth of the fermenting strain C. pseudotropicalis 11, furfural (0.04%) did not exhibit stable inhibitory effect on the enzyme activities of NADPH-GDH, NADH-GDH, GS, GOGAT and ADH. To the opposite, when reaching the steady state after furfural addition, their activities increased 6.3, 4.9, 5.6 and 4.1 times, respectively. At D = 0.25 h−1, GS activity was stronger affected by the dilution rate. Furfural did not inhibit the activity of NADPH-GDH, NADH-GDH and ADH. However, continuous inhibitory effect on GS and GOGAT activity was observed.