Zinc(II) binding to apo-(bovine erythrocyte superoxide dismutase).

The binding of zinc(II) ions to apo-(bovine erythrocytes superoxide dismutase) was studied by 1H n.m.r. spectroscopy. Two zinc(II) ions bind to each subunit of the apoenzyme, and the first has a binding constant at least an order of magnitude larger than the second. The nature of the spectral changes that occur on binding the first zinc(II) ion are interpreted in terms of a change in the structure of the protein around the active site to one very similar to that of the holoenzyme, thus pre-forming the second zinc(II) binding site. The binding of the second zinc(II) ion effects changes in the environment of only those residues involved in its co-ordination.