Relaxometric characterization of human hemalbumin

Mauro Fasano, Simona Baroni, Alessandro Vannini, Paolo Ascenzi, Silvio Aime

Research output: Contribution to journalArticle


Hemalbumin [i.e., Fe(III)-protoporphyrin IX-human serum albumin; Fe(III)heme-HSA] is an important intermediate in the recovery of heme iron following hemolysis. Relaxometric data are consistent with the occurrence of a hexacoordinated high-spin Fe(III) center with no water in the inner coordination sphere. The relatively high relaxation enhancement observed for an aqueous solution of Fe(III)heme-HSA (r1p=4.8 mM-1 s-1 at 20 MHz, pH 7, and 25°C) is ascribed to the occurrence of a strong contribution from water molecules in the second coordination sphere. Structural analysis of the putative binding region has been performed by a Monte Carlo simulated annealing procedure, which allowed us to identify His105 and Tyr148 as axial ligands. The role of a tyrosinate as the sixth Fe(III)heme ligand is supported by the pH-dependent analysis. Interestingly, when Fe(III) is replaced by Mn(III), the occurrence of a fast exchanging water molecule at pH values close to neutrality is detected. As the pH is increased, the Mn(III) containing system behaves analogously to Fe(III)heme-HSA. At higher pH, the phenolate ligand is eventually displaced by OH- from both Fe(III) and Mn(III) centers. Support for the proposed bonding scheme has been gained also from competitive binding assays for the sixth coordination site by fluoride, azide, and imidazole ligands.

Original languageEnglish
Pages (from-to)650-658
Number of pages9
JournalJournal of Biological Inorganic Chemistry
Issue number5-6
Publication statusPublished - 2001


  • Albumin
  • Binding
  • Hemalbumin
  • NMR dispersion
  • Proton relaxation

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Biochemistry

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    Fasano, M., Baroni, S., Vannini, A., Ascenzi, P., & Aime, S. (2001). Relaxometric characterization of human hemalbumin. Journal of Biological Inorganic Chemistry, 6(5-6), 650-658.