Parameters screened for optimization Final hydrogen concentration (mM) No optimization 112 Enzyme degradation (λ) 118 Enzyme affinity for substrate (Km) 238 Initial enzyme concentration (E0) 591 Enzyme turn-over (kcat) 810

Table 1: Hydrogen final concentration value reached by the system after single stage optimization runs. E0, kcat, Km and λ for all the 13 enzymes were optimized each separately while the other parameters were kept constant at their default values (see Method). The modifications were evaluated in order to obtain the best final hydrogen concentration (mM) after a simulation time of 9000 min with starting concentrations of 70 mM for cellobiose, 70 mM for inorganic phosphate and 1 mM for NADP. Additional results are featured in Figure 3.