Spectroscopic analysis of the interaction between chromium (III) and apoovotransferrin

Ovotransferrin (OTf) is a main member of the transferrin family that functions both as an iron transporter and an antibacterial agent. In this study, the thermodynamic property of the interaction between chromium (III) and ovotransferrin was investigated. The conditional binding constants for Cr3+ binding to the protein were determined by difference UV spectroscopy and were found to be log KC=13.08±0.24 and log KN=5.65±0.12. It was found that Cr3+ preferentially binds to the C-terminal site over the N-terminal site under these experimental conditions. The conformational changes in apoovotransferrin (apoOTf) during Cr3+ binding were studied by fluorescence spectroscopy using 2-p-toluidinylnaphthalene-6-sulfonate (TNS) as the fluorescence probe and by circular dichroism (CD) spectroscopy. The results show that a large conformational change in apoOTf can be attributed to binding of Cr3+ to the N-terminal site, instead of the C-terminal site. In addition, the binding of Cr3+ to apoOTf stabilizes the structure of OTf as determined by guanidine hydrochloride denaturation studies. These findings help advance our understanding of the biological effects of Cr3+.