Abstract
Abstract Conalbumin complexes containing one, and only one, specifically bound metal ion were isolated by the isoelectric focusing technique. This made possible the preparation of a series of mixed metal or mixed isotope complexes: GaoFeiconalbumin, FeoGaiconalbumin, 56Fe2conalbumin, 56Feo 57Feiconalbumin, 57Feo 56Feiconalbumin, and 57Fe2conalbumin. The appropriate species were studied by EPR, Mossbauer, and optical spectroscopy. It was possible, in this way, to determine the contribution of each site to the spectrum of the protein. Occupancy of the first (or inner) binding site by Fe(III) produces EPR, Mossbauer, and optical difference spectra which are readily distinguishable from those given by the second (outer) site. Summation spectra obtained from the two sites are the same as those obtained from diferric conalbumin. We conclude, therefore, that the specific binding sites of conalbumin are not identical, and that the protein does not bind metal ions in a simple random fashion.
Highlights
The characteristic optical spectra produced by the binding of metal ions are t,he same for conalbumin and human plasma transferrin, and the thermodynamics of metal binding are similar but probably not identical for the two proteins [3, 4]
The present study was undertaken to determine whether this line reflects a difference between the binding sites of conalbumin that is not evident in transferrin; and whet.her such a possibility could be corroborated by Mijssbauer and optical spectroscopy
In order to see the spectra of bound iron without interference from tyrosyl ionization in the protein, the difference spectra of Ga,Feiconalbumin (C, C’) and Fe,Ga;conalbumin (D, D’) were read against digallium conalbumin, i.e. in all samples both binding sites were occupied by trivalent metal ions
Summary
Conalbumin complexes containing one, and only one, bound metal ion were isolated by the isoelectric focusing technique. The characteristic optical spectra produced by the binding of metal ions are t,he same for conalbumin and human plasma transferrin, and the thermodynamics of metal binding are similar but probably not identical for the two proteins [3, 4]. The present study was undertaken to determine whether this line reflects a difference between the binding sites of conalbumin that is not evident in transferrin; and whet.her such a possibility could be corroborated by Mijssbauer and optical spectroscopy. In the approach we have chosen, conalbumin bearing a single metal ion is isolat.ed and studied spectroscopically To this preparation a 2nd metal ion is added, and the spectral properties of this complexed ion are determined directly or by difference spectroscopy.
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