TRANSFERRIN, A MECHANISM FOR THE HOLOPROTEIN FORMATION FROM NITRILOTRIACETATO-FE(III)-TRANSFERRIN MIXED COMPLEX

Holotransferrin formation from the mixed transferrin-nitrilotriacetato Fe(III) iron complex (THFeL) in the presence of carbonate has been inv estigated between pH 6.5 and 8.5. Both C- and N-sites seem equivalent towards tile interaction with bicarbonate. Bicarbonate interacts with THFeL to yield a new mixed complex, T'H(2)FeL; apparent rate constant, 2.25 s(-1). T'H(2)FeL, then, loses two protons and the nitrilotriacet ate ligand to yield the holoprotein, T'Fe; the two protons dissociatio n constant, K-a = 4.35 X 10(-15) M(2). This is accompanied by a gain o f about tell orders of magnitude in the stability of the iron-protein complex and can be of interest for a better understanding of iron-upta ke by the protein in natural media.