ULTRAVIOLET DIFFERENCE SPECTRAL STUDIES OF CONALBUMIN COMPLEXES WITH TRANSITION METAL IONS

Evidence was sought for the binding of various transition metal ions to hen's egg conalbumin using ultraviolet difference spectroscopy. Difference spectra of metalconalbumin vs. conalbumin were recorded in the 230-320- mμ region at pH 8.5. In addition to the known binding of Fe3+, Cu2+, and Zn2+ to conalbumin, Cr3+, Mn2+, Co2+, Ni2+, and Cd2+ were found to react with the two specific binding sites of the protein. The difference spectra were characterized by two maxima near 245 and 295 mμ. The Xmax and emax depended upon the specific metal bound. These spectral shifts may be attributed to perturbations caused by the binding of different metal ions to the tyrosyl residues of the binding sites and by the involvement of ligands other than tyrosine in the metalconalbumin binding. The increase in absorbance at 245 and 295 mμ on binding of metal ions by conalbumin revealed that two tyrosyl residues are coordinated to each trivalent metal ion whereas one tyrosyl residue is coordinated to each divalent metal ion. Displacement of bound metal by other metal ions showed that the relative stability of the transition metal conalbumin complexes is in the following order: Fe3+ > rCr3+ Cu2+ > Mn2+, Co2+, Cd2+ > Zn2+> Ni2+. © 1969, American Chemical Society. All rights reserved.