Reversible protonation of a thiolate ligand in an [Fe]-hydrogenase model complex

The thiolate ligand in the five-coordinate model complex 1 of [Fe]-hydrogenase is preferentially and reversibly protonated, even in the presence of an acyl ligand. The results suggest that the Cys176 thiolate ligand in [Fe]-hydrogenase can serve as the internal base to accept the proton after heterolytic splitting of H2.