The Kinetics and Mechanism of Iron(III) Exchange between Chelates and Transferrin

Abstract

Abstract The rate of exchange of iron from ethylenediaminetetraacetate has been studied. The substance initially formed has a spectral absorption maximum at 520 mµ. In time, this peak shifts to 470 mµ, characteristic of the transferrin-iron complex. These results suggest the initial formation of an EDTA-iron-transferrin complex. Kinetic studies as a function of ferric EDTA and of apotransferrin concentrations are consistent with such a mechanism. The rate of removal of iron from ferric transferrin was in the order EDTA g citrate g nitrilotriacetic acid. The latter two chelates, however, reached equilibrium more rapidly. The importance of steric effects, as well as stability constants, in the biological utilization of trace metals is emphasized.