Metabolic flux analysis of Saccharomyces cerevisiae during redox potential-controlled very high-gravity ethanol...

A previously published genome-scale metabolic model namely iFF708 was modified to depict the metabolic flux distribution within Saccharomyces cerevisiae grown under a redox potential-controlled very high-gravity condition. The following modifications were made: electron transport chain (ETC) and oxidative phosphorylation, proton gradient and ATP transportation, and malate-aspartate shuttle. With these modifications, this model could describe the experimental data collected from the above-mentioned ethanol fermentation. As a result, the simulation unveiled that the P/O ratio is critical under microaerobic conditions and the malate-aspartate shuttle is inactivated due to the shortage of electron transport across mitochondria. In other words, the limited supply of oxygen suppresses the functionality of oxidative phosphorylation, tricarboxylic acid (TCA) cycle, and ETC. In terms of the glycolytic pathway, fluxes coming from glucose-6-phosphate and pyruvate nodes are insensitive to the changes of fermentation redox potential. As the initial glucose concentration is greater than 250 g/L, the interactive effect between the initial glucose concentration and redox potential level becomes noticeable.