Warfarin modulates the nitrite reductase activity of ferrous human serum heme-albumin

Paolo Ascenzi, Grazia R. Tundo, Gabriella Fanali, Massimo Coletta, Mauro Fasano

Research output: Contribution to journalArticlepeer-review


Human serum heme-albumin (HSA-heme-Fe) displays reactivity and spectroscopic properties similar to those of heme proteins. Here, the nitrite reductase activity of ferrous HSA-heme-Fe [HSA-heme-Fe(II)] is reported. The value of the second-order rate constant for the reduction of NO- 2 to NO and the concomitant formation of nitrosylated HSA-heme-Fe(II) (i.e., kon) is 1.3 M-1 s-1 at pH 7.4 and 20 °C. Values of kon increase by about one order of magnitude for each pH unit decrease between pH 6.5 to 8.2, indicating that the reaction requires one proton. Warfarin inhibits the HSA-heme-Fe(II) reductase activity, highlighting the allosteric linkage between the heme binding site [also named the fatty acid (FA) binding site 1; FA1] and the drug-binding cleft FA2. The dissociation equilibrium constant for warfarin binding to HSA-heme-Fe(II) is (3.1 ± 0.4) × 10-4 M at pH 7.4 and 20 °C. These results: (1) represent the first evidence for the NO- 2 reductase activity of HSA-heme-Fe(II), (2) highlight the role of drugs (e.g., warfarin) in modulating HSA(-heme-Fe) functions, and (3) strongly support the view that HSA acts not only as a heme carrier but also displays transient heme-based reactivity.

Original languageEnglish
Pages (from-to)939-946
Number of pages8
JournalJournal of Biological Inorganic Chemistry
Issue number8
Publication statusPublished - 2013


  • Allostery
  • Ferrous human serum heme-albumin
  • Inhibition by warfarin
  • Kinetics
  • Nitrite reductase activity

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry


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