Transferrin, a mechanism for the holoprotein formation from nitrilotriacetato-Fe(III)-transferrin mixed complex

Abstract

Holotransferrin formation from the mixed transferrin-nitrilotriacetatoFe(III) iron complex (THFeL) in the presence of carbonate has been investigated between pH 6.5 and 8.5. Both C- and N-sites seem equivalent towards the interaction with bicarbonate. Bicarbonate interacts with THFeL to yield a new mixed complex, T’H2FeL; apparent rate constant, 2.25 s-1. T’H2FeL, then, loses two protons and the nitrilotriacetate ligand to yield the holoprotein, T’Fe; the two protons dissociation constant, Ka = 4.35 X 10-15 M2. This is accompanied by a gain of about ten orders of magnitude in the stability of the iron-protein complex and can be of interest for a better understanding of iron-uptake by the protein in natural media.