Reductive nitrosylation of ferric cyanide horse heart myoglobin is limited by cyanide dissociation

Paolo Ascenzi, Alessandra di Masi, Francesca Gullotta, Marco Mattu, Chiara Ciaccio, Massimo Coletta

Research output: Contribution to journalArticle


Cyanide binds to ferric heme-proteins with a very high affinity, reflecting the very low dissociation rate constant (koff). Since no techniques are available to estimate koff, we report herewith a method to determine koff based on the irreversible reductive nitrosylation reaction to trap ferric myoglobin (Mb(III)). The koff value for cyanide dissociation from ferric cyanide horse heart myoglobin (Mb(III)-cyanide) was determined at pH 9.2 and 20.0 °C. Mixing Mb(III)-cyanide and NO solutions brings about absorption spectral changes reflecting the disappearance of Mb(III)-cyanide with the concomitant formation of ferrous nitrosylated Mb. Since kinetics of reductive nitrosylation of Mb(III) is much faster than Mb(III)-cyanide dissociation, the koff value, representing the rate-limiting step, can be directly determined. The koff value obtained experimentally matches very well to that calculated from values of the second-order rate constant (kon) and of the dissociation equilibrium constant (K) for cyanide binding to Mb(III) (koff = kon × K).

Original languageEnglish
Pages (from-to)196-200
Number of pages5
JournalBiochemical and Biophysical Research Communications
Issue number2
Publication statusPublished - Mar 5 2010


  • Ferric cyanide horse heart myoglobin
  • Kinetics
  • Nitrogen monoxide
  • Reductive nitrosylation

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Cell Biology
  • Molecular Biology

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