Nickel hydrogenases ligand environment

Many biomolecules feature metal ions in a mixed donor set, and the area is intensively studied. As an example, the active site of the hydrogenase from thiocapsa roseopersicina features nickel in a mixed 0,N,S donor environment. Definition of the ligand donor set in biopolymers is not always facile, however, so they tend to be overlooked as examples of mixed donor ligands. There are some small biomolecule examples extant. 

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