Table 2.

Maximum impact of different pathway engineering strategies for improving ethanol yields, estimated with a stoichiometric model of the core metabolic network of S. cerevisiae [117]. Assumptions on biomass composition, maintenance-energy requirements, as well as modifications to the model that were implemented to simulate each of the metabolic engineering strategies, are described in Supplementary Materials. For the strategies focused on NADH re-oxidation, glycerol production was set at zero and oxidation of surplus NADH from biosynthetic reactions was entirely routed through the engineered pathways.

Specific growth rate (h−1)	Yethanol/hexose (mol/mol)
	Reference	Altered ATP coupling of sugar dissimilation		Alternative pathways for re-oxidation of NADH
	Wild type	H+ symport/intracellular hydrolysis of sucrose (yields 1.5 ATP/hexose)	H+ symport of glucose (yields 1 ATP/glucose)	PFL/A-ALD	PK/PTA/A-ALD	PRK/Rubisco
0.3	1.51	1.63 (8.1%)	1.76 (16.2%)	1.64 (8.7%)	1.66 (9.7%)	1.69 (11.9%)
0.1	1.54	1.66 (7.5%)	1.77 (14.9%)	1.67 (8.4%)	1.69 (9.5%)	1.71 (11.3%)
0.03	1.62	1.72 (5.8%)	1.81 (11.6%)	1.74 (7.4%)	1.76 (8.5%)	1.78 (9.5%)
0.01	1.75	1.81 (3.6%)	1.87 (7.2%)	1.84 (5.2%)	1.86 (6.1%)	1.86 (6.4%)
0.001	1.95	1.97 (0.6%)	1.98 (1.2%)	1.97 (1.0%)	1.98 (1.2%)	1.98 (1.2%)