TABLE 2.
Equilibrium hydrogen concentrations produced by HydAB with varied NADH/NAD+ ratios.
| Conditiona | Ratio of NADH/NAD+ | Predicted equilibrium hydrogen partial pressure (Pa)d | Observed hydrogen partial pressure (Pa)b | Hydrogen produced (nanomol)b |
| 1.0 mM NAD+ + 5.0 mM NADH | 5.0 | 105.9 | 40.2 ± 3.2 | 101.8 ± 8.1 |
| 3.0 mM NAD+ + 3.0 mM NADH | 1.0 | 21.3 | 9.1 ± 2.4 | 23.2 ± 6.0 |
| 5.0 mM NAD+ + 1.0 mM NADH | 0.2 | 4.24 | 2.2 ± 0.4 | 5.4 ± 1.1 |
| 0.0 mM NAD+ + 0.0 mM NADH | NAc | NA | 0.4 ± 0.2 | 1.0 ± 0.6 |
aAssays were performed at pH 7.5 in 6.5 ml serum bottles with 1.0 ml of liquid volume containing 69.6 μg of HydAB and 5.5 ml of headspace. bValues are the mean ± the standard deviation of triplicate assays. cNA, not applicable. dPredicted equilibrium concentrations of hydrogen were calculated as described by Gutekunst and Schulz (2018). Equation and terms used were: e((–0.094⋅n ⋅F)/(R⋅T)) [NADH/NAD+] ⋅ 10(–pH +7) = [pH2]. F (Faraday’s constant) = 96.485 J ⋅ V–1 ⋅ mol–1 of electron equivalents. R (Gas Constant) = 8.314 J ⋅ K ⋅ mol–1. n = 2, number of e– in transfer reaction. T = 298.15 Kelvin. [pH2] = Partial pressure of hydrogen −0.094 = ΔE′, difference in standard reduction potentials of [H+/H2] = −414 mV and [NADH/NAD+] = −320 mV.