Transferrin binding Al3+ and Fe3+

R. B. Martin, J. Savory, S. Brown, R. L. Bertholf, M. R. Wills

Research output: Contribution to journalArticlepeer-review

216 Scopus citations


An understanding of Al3+-induced diseases requires identification of the blood carrier of Al3+ to the tissues where Al3+ exerts a toxic action. Quantitative studies demonstrate that the protein transferrin (iron-free) is the strongest Al3+ binder in blood plasma. Under plasma conditions of pH 7.4 and [HCO3-]27 mmol/L, the successive constant values for Al3+ binding to transferrin are log K1 = 12.9 and log K2 = 12.3. When the concentration of total Al3+ in plasma is 1 μmol/L, the free Al3+ concentration permitted by transferrin is 10-14.6 mol/L, less than that allowed by insoluble Al(OH)3, by Al(OH)2H2PO4, or by complexing with citrate. Thus transferrin is the ultimate carrier of Al3+ in the blood. We also used intensity changes produced by metal ion binding to determine the stability constants for Fe3+ binding to transferrin: log K1 = 22.7 and log K2 = 22.1. These constants agree closely with a revision of the reported values obtained by equilibrium dialysis. By comparison with Fe3+ binding, the Al3+ stability constants are weaker than expected; this suggests that the significantly smaller Al3+ ions cannot coordinate to all the transferrin donor atoms available to Fe3+.

Original languageEnglish (US)
Pages (from-to)405-407
Number of pages3
JournalClinical Chemistry
Issue number3
StatePublished - 1987

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Biochemistry, medical


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