Redox balances in the metabolism of sugars by yeasts. (NAD(H); NADP(H); glucose metabolism; xylose fermentation; ethanol; Crabtree effect; Custers effect)

Applied Science

Beijerinck Centennial Microbial Physiology and Gene Regulation: Emerging Principles and Applications

Book of abstracts of Beijerinck Centennial Microbial Physiology and Gene Regulation: Emerging Principles and Applications, 10-14 December 1995 The Hague, The Netherlands. Under the auspices of the Netherlands Foundation for Biotechnology.Applied Science

A theoretical analysis of NADPH production and consumption in yeasts

Theoretical calculations of the NADPH requirement for yeast biomass formation reveal that this parameter is strongly dependent on the carbon and nitrogen source. The data obtained have been used to estimate the carbon flow over the NADPH-producing pathways in these organisms, namely the hexose monophosphate pathway and the NADP+-linked isocitrate dehydrogenase reaction. It was calculated that during growth of yeasts on glucose with ammonium as the nitrogen source at least 2% of the glucose metabolized has to be completely oxidized via the hexose monophosphate pathway for the purpose of NADPH synthesis. This figure increases to approximately 20% in the presence of nitrate as the nitrogen source. Not only during growth on glucose but also on other substrates such as xylose. methanol, or acetate the operation of the hexose monophosphate pathway as a source of NADPH is essential, since the N ADP+-isocitrate dehydrogenase reaction alone cannot meet the NADPH demand for anabolism. NADPH production via these pathways requires an expenditure of ATP. Therefore, the general assumption made in calculations of the ATP demand for biomass formation that generation of NADPH does not require energy is, at least in yeasts, not valid.Applied Science