Loss of chromium(III) from mixed Cr(III),Fe(III) serum Transferrins

Abstract

Trivalent chromium has been shown to be transported in vivo from the bloodstream to the tissues via endocytosis by transferrin (Tf), the major iron transport protein in the blood. Recent in vitro studies using Cr(III)₂-Tf have shown that under physiologically relevant conditions, the binding of Cr(III) to Tf and the loss of Cr(III) from the Cr(III)₂-Tf/Tf receptor complex are rapid. However, the major form of transferrin in the bloodstream is monoferric Tf. Thus, given the low concentrations of Cr(III) in the bloodstream, the form of Cr(III)-containing transferrin in the bloodstream that is transported via endocytosis is monochromic, monoferric-Tf (Cr(III),Fe(III)-Tf). Given that Tf has two specific metal-binding sites, one in both the C-terminal and the N-terminal lobes of Tf, two forms of Cr(III),Fe(III)-Tf can form. The loss of Cr(III) from both forms of Cr(III),Fe(III)-Tf have been examined for the first time. The mixed metal Tf's lose Cr(III) in similar fashions to Cr(III) losses from Cr(III)₂-Tf itself or from the Cr(III)₂-Tf/Tf receptor complex.

Keywords: Chromium; Endocytosis; Iron; Transferrin; Transferrin receptor; Transport.