Identification of a Ni- and Fe-containing cluster in Rhodospirillum rubrum carbon monoxide dehydrogenase

Methyl viologen-oxidized carbon monoxide dehydrogenase (CODH) from Rhodospirillum rubrum exhibits complex EPR. Comparison to EPR of oxidized apo-CODH (CODH from which Ni is lacking) leads to the identification of signals whose intensity is correlated with the presence of Ni. 61Ni labeling observably broadens the sharpest feature of these signals, as does 57Fe. R. rubrum CODH thus contains a cluster containing both Ni and Fe. The EPR associated with this cluster is unlike any EPR previously attributed to Ni-containing prosthetic groups in other CODH enzymes or Ni-containing hydrogenases. The CO-analogue, CN-, perturbs the EPR signals that are attributed to the Ni-Fe species.