Charge-site communication in proteins: Electrostatic heme linkage of azide binding by sperm whale myoglobin

Stephen H. Friend, Keith L. March, George I H Hanania, Frank R N Gurd

Research output: Contribution to journalArticle

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Abstract

The binding of azide ion to sperm whale ferrimyoglobin has been measured at 25°C over the pH range 4.0-6.0 at ionic strengths 0.001, 0.002, 0.005, and 0.010 M. The pH dependence of the binding constant, kL, was analyzed in terms of the modified discrete charge electrostatic theory in three ways. First, an "independent-site" model was constructed in which the charged sites that interact with the charged heme iron, and which lose that interaction on neutralization of the iron charge in the azide complex, are considered not to interact with each other. This unrealistic analysis of the heme linkage fails to conform to the experimental results. The subsequent analyses employed the full electrostatic treatment in which each site is taken to interact with each other as well as with the charge borne by the iron. Second, the increase, Δν̄, in binding of hydrogen ions accompanying the azide binding was estimated from the experimental pH dependence of log kL and compared with that computed in terms of the theoretical predictions of the changes in pK values accompanying binding. The agreement was satisfactory under all conditions studied, with divergence of about 25% at most. Third, the observed pH dependence of log kL for each ionic strength was described within 0.10 unit in terms of the summed changes in electrostatic free energy for each charge site accompanying the azide binding as sensed at the iron binding site. The contributions attributed to the individual charged groups were most important where their static solvent accessibilities are low. In these terms, the effective electrostatic domain for interactions with the heme site corresponds to nearly the whole of the myoglobin molecule.

Original languageEnglish
Pages (from-to)3039-3047
Number of pages9
JournalBiochemistry
Volume19
Issue number13
StatePublished - 1980

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Sperm Whale
Azides
Myoglobin
Static Electricity
Heme
Electrostatics
Iron
Communication
Ionic strength
Osmolar Concentration
Proteins
Metmyoglobin
Free energy
Protons
Binding Sites
Ions
Molecules

ASJC Scopus subject areas

  • Biochemistry

Cite this

Friend, S. H., March, K. L., Hanania, G. I. H., & Gurd, F. R. N. (1980). Charge-site communication in proteins: Electrostatic heme linkage of azide binding by sperm whale myoglobin. Biochemistry, 19(13), 3039-3047.

Charge-site communication in proteins : Electrostatic heme linkage of azide binding by sperm whale myoglobin. / Friend, Stephen H.; March, Keith L.; Hanania, George I H; Gurd, Frank R N.

In: Biochemistry, Vol. 19, No. 13, 1980, p. 3039-3047.

Research output: Contribution to journalArticle

Friend, SH, March, KL, Hanania, GIH & Gurd, FRN 1980, 'Charge-site communication in proteins: Electrostatic heme linkage of azide binding by sperm whale myoglobin', Biochemistry, vol. 19, no. 13, pp. 3039-3047.
Friend, Stephen H. ; March, Keith L. ; Hanania, George I H ; Gurd, Frank R N. / Charge-site communication in proteins : Electrostatic heme linkage of azide binding by sperm whale myoglobin. In: Biochemistry. 1980 ; Vol. 19, No. 13. pp. 3039-3047.
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