Nitrile Hydratase from Rhodococcus rhodochrous J1 Contains a Non-Corrin Cobalt Ion with Two Sulfur Ligands

Abstract

We present spectroscopic data that show that a nitrile hydratase from Rhodococcus rhodochrous J1 is the first reported example of a native protein that contains a non-corrin Co{sup 3+} ion with a mixed S and N(O) ligand field. The similarities of the pre-edge and EXAFS spectra suggest that the ligand environments of the metal ions in the cobalt- and the iron-containing nitrile hydratases are very similar. Low-spin six-coordinate CO{sup 3+} complexes show S {yields} Co{sup 3+} charge transfer transitions at approximately 280 nm. Although featureless in the visible region, the absorption spectrum of nitrile hydratase from R. rhodochrous J1 (data not shown) has a significant shoulder above 300 nm that we suggest may have S {yields} Co ligand-to-metal charge transfer character. The absence of coenzyme B{sub 12} in the enzyme is shown by the lack of corrin absorbance in the visible spectrum and by the strong similarity in metal sites in the iron- and cobalt-containing nitrile hydratases revealed by EXAFS. Although there are several naturally occurring non-corrin Co{sup 2+} enzymes, the nitrile hydratase from R. rhodochrous J1 is the first example, to our knowledge, of a native non-corrin Co{sup 3+} enzyme as well as of biological Co-S coordination. 28 refs.,more » 3 figs.« less