Pressure Dependence of the Intramolecular Electron Transfer Reaction in Myoglobin Reinvestigated

Yoshiaki Furukawa, Koichiro Ishimori, Isao Morishima

Research output: Contribution to journalArticle

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Abstract

The activation volumes (ΔV) for intramolecular electron transfer (ET) reactions in Ru-modified Zn-porphyrin (ZnP) substituted myoglobins (Ru-ZnMb) have been determined to investigate the pressure effects on the redox potentials and donor-acceptor distance (D-A distance) for the ET reaction. Three Ru-ZnMbs, in which D-A distances for the ET reactions are 12.7 Å (His48Mb), 15.5 Å (His83Mb), and 19.3 Å (His81Mb), were constructed. The activation volumes for the forward ET reactions (ΔVf) were -1.6 (His83Mb), +3.7 (His81Mb), and +6.5 cm3 mol-1 (His48Mb). We also measured the pressure dependence of the back ET reactions (from Ru2+ complex to ZnP+), showing that the back ET reactions exhibited negative activation volumes (ΔVb) for all of the Ru-ZnMbs: -11, -5.3, and -6.2 cm3 mol-1 for His83Mb, His81Mb, and His48Mb, respectively. On the basis of these activation volumes, the pressure dependence of the redox potentials, (∂ΔG°/∂P)T, was estimated as about 2.94 × 10-4 eV MPa-1, regardless of the position of the Ru complex. Since (∂ΔG°/∂P)T in the present study is close to that of Ru(NH3)62+/3+ (2.97 × 10-4 eV MPa-1), the pressure-induced redox changes of the Ru complex were primarily responsible for that of the ET reaction and the contribution of ZnP to the pressure dependence of the redox potential on the ET reactions would be small. In sharp contrast to (∂ΔG°/∂P)T, the pressure dependence of the D-A distance, (∂d/∂P)T, highly depends on the ET pathway and microenvironments of the redox centers. The linear compressibility, (-1/d0)(∂d/∂P)T, was (2.2 ± 0.1) × 10-10, (5.1 ± 0.5) × 10-11, and (-2.6 ± 3.2) × 10-11 m2 N-1 for His83Mb, His81Mb, and His48Mb, respectively. The different linear compressibility for the three ET reaction systems suggests that the structural fluctuation in proteins is not unique in protein structure and site specific local fluctuations would be one of the factors regulating the protein ET reactions.

Original languageEnglish
Pages (from-to)1817-1825
Number of pages9
JournalJournal of Physical Chemistry B
Volume104
Issue number8
Publication statusPublished - 2000 Mar 2
Externally publishedYes

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myoglobin
Myoglobin
pressure dependence
electron transfer
Electrons
Porphyrins
Chemical activation
porphyrins
activation
proteins
Proteins
Compressibility
compressibility
Pressure effects
pressure effects
Oxidation-Reduction

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Pressure Dependence of the Intramolecular Electron Transfer Reaction in Myoglobin Reinvestigated. / Furukawa, Yoshiaki; Ishimori, Koichiro; Morishima, Isao.

In: Journal of Physical Chemistry B, Vol. 104, No. 8, 02.03.2000, p. 1817-1825.

Research output: Contribution to journalArticle

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N2 - The activation volumes (ΔV≠) for intramolecular electron transfer (ET) reactions in Ru-modified Zn-porphyrin (ZnP) substituted myoglobins (Ru-ZnMb) have been determined to investigate the pressure effects on the redox potentials and donor-acceptor distance (D-A distance) for the ET reaction. Three Ru-ZnMbs, in which D-A distances for the ET reactions are 12.7 Å (His48Mb), 15.5 Å (His83Mb), and 19.3 Å (His81Mb), were constructed. The activation volumes for the forward ET reactions (ΔV≠f) were -1.6 (His83Mb), +3.7 (His81Mb), and +6.5 cm3 mol-1 (His48Mb). We also measured the pressure dependence of the back ET reactions (from Ru2+ complex to ZnP+), showing that the back ET reactions exhibited negative activation volumes (ΔV≠b) for all of the Ru-ZnMbs: -11, -5.3, and -6.2 cm3 mol-1 for His83Mb, His81Mb, and His48Mb, respectively. On the basis of these activation volumes, the pressure dependence of the redox potentials, (∂ΔG°/∂P)T, was estimated as about 2.94 × 10-4 eV MPa-1, regardless of the position of the Ru complex. Since (∂ΔG°/∂P)T in the present study is close to that of Ru(NH3)62+/3+ (2.97 × 10-4 eV MPa-1), the pressure-induced redox changes of the Ru complex were primarily responsible for that of the ET reaction and the contribution of ZnP to the pressure dependence of the redox potential on the ET reactions would be small. In sharp contrast to (∂ΔG°/∂P)T, the pressure dependence of the D-A distance, (∂d/∂P)T, highly depends on the ET pathway and microenvironments of the redox centers. The linear compressibility, (-1/d0)(∂d/∂P)T, was (2.2 ± 0.1) × 10-10, (5.1 ± 0.5) × 10-11, and (-2.6 ± 3.2) × 10-11 m2 N-1 for His83Mb, His81Mb, and His48Mb, respectively. The different linear compressibility for the three ET reaction systems suggests that the structural fluctuation in proteins is not unique in protein structure and site specific local fluctuations would be one of the factors regulating the protein ET reactions.

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