Figure 1

Schematic representation of central carbon metabolism and the introduced Calvin-cycle enzymes in Saccharomyces cerevisiae . Orange: Formation of biomass and NADH from glucose and NADPH. Stoichiometries are according to Verduyn et al.[7]; Blue: Redox-neutral, ATP-yielding alcoholic fermentation of glucose and galactose via the Embden-Meyerhof-Parnas glycolysis and Leloir pathways, respectively; Magenta: NADPH generation via the oxidative part of the pentose-phosphate pathway; Green: rearrangement of sugar-phosphate carbon skeletons via the non-oxidative pentose-phosphate pathway; Black: NADH oxidation by formation of glycerol through glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase; Red: heterologously expressed Calvin-cycle enzymes phosphoribulokinase and Rubisco. Numbers in boxes represents the distribution of carbon along the different pathways (in mmol) normalized for a combined glucose and galactose uptake of 100 mmol for a wild-type, glycerol-producing reference strain (top) and for a scenario in which the alternative pathways via the Calvin cycle enzymes completely replace glycerol formation as the mechanism for reoxidizing NADH formed in biosynthetic reactions (bottom). In the scenario with the Calvin cycle enzymes, ribulose-5-phosphate was assumed to be preferentially derived from the oxidative reactions of the pentose phosphate pathway. Once the generation of NADPH from these reactions matched the requirement for NADPH in biosynthesis, further ribulose-5-phosphate was derived from glycolytic intermediates via the non-oxidative pentose-phosphate pathway rearrangement reactions. The biomass yield on ATP was assumed to be identical for both scenarios.