Figure 11.

(A) pH dependence of the relative populations of Ni_a-C (purple circles), Ni_a-L_II (orange triangles), and Ni_a-L_III (orange diamonds) states as determined from the respective ν_CO band intensities in a series of PFIRE measurements similar to those previously reported.³⁶ The Ni_a-L states of E. coli Hyd-1 do not share the same pH dependence, implying multiple protonation sites, or multiple orientations of the same protonation site. (B) Conformational flexibility of a conserved glutamate (Glu13 in A. aeolicus Hase 1 numbering, Glu28 in E. coli Hyd-1 numbering, circled in red) has been suggested on the basis of molecular dynamics simulations in Group 1 O₂-tolerant hydrogenases; the two conformations are shown in orange and purple. Panel (B) reproduced with permission from ref (112). Copyright 2014 American Chemical Society.