Figure 2: Population of Hhyd in HydA1 by simultaneously increasing H2 and H+ pressure.
From: Accumulating the hydride state in the catalytic cycle of [FeFe]-hydrogenases
(a) ATR FTIR difference spectrum (N2/pH8→H2/pH8), depicting the accumulation of the reduced states (Hred/Hred and Hsred) in the catalytic cycle of HydA1 under H2 at pH 8. (c) ATR FTIR difference spectrum (N2/pH8→H2/pH4) depicting the accumulation of Hhyd in the catalytic cycle of HydA1 under H2 at pH 4. Catalytic cycles (b,d) beside the corresponding spectra illustrate the shift in steady-state equilibrium depending on applied substrate and product pressures in the working model of the catalytic cycle, which comprises the already-characterized states Hox, Hred/Hred and Hsred, and the missing H2-activated state (Hhyd). Peak labels for Hox are presented in black, for Hhyd in blue, for Hred in green and for Hsred in magenta (red asterisks: Hred). For the complete state-specific CN−-/CO-vibrational spectra of HydA1 observed during sample analysis, see Supplementary Table 1. At pH 4, the vibrational signals of Hox were slightly shifted to higher frequencies (for more information see Supplementary Table 1, Hox-blue).
