CD-113 AND C-13 NMR OF CADMIUM(II) TRANSFERRINS

The cadmium(I1) derivatives of ovotransferrin and human serum transferrin have been investigated through '13Cd and I3C NMRspectroscopy. A sharp llJCd signal due to the bound Cd(I1) ion is observed at 21.6 and 11.7 ppm for ovotransferrin and humanserum transferrin, respectively. These chemical shift values are consistent with the involvement of only one histidine in eachmetal-binding set of the protein, as indicated by the recent X-ray structure of human lactoferrin. In the I3C NMR spectra theprotein-bound carbonate signal is found in both cases at 168.2 ppm, and it clearly splits into a doublet ( J - 20 Hz) when theprotein contains "'Cd-enriched cadmium, thus giving further evidence of direct metal-carbonate binding. The addition of thenonsynergistic anion perchlorate to the ovotransferrin derivative resulted in the removal of the bound cadmium