Temperature and viscosity dependence of the electron-transfer reaction between plastocyanin and cytochrome c labeled with a ruthenium(II) bipyridine complex

Harris, Michele R.; Davis, Danny J.; Durham, Bill; Millett, Francis

doi:10.1016/s0005-2728(96)00155-7

Cited by 17 publications

(13 citation statements)

References 8 publications

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“…The value for the protein friction (σ ) 4.0 cP) is comparable to the values measured for the ZnCc-plastocyanin and ZnCc-cytochrome b 5 complexes (3)(4)(5). The activation parameters (∆H q ) 22.6 ( 1.4 kJ/mol and ∆S q ) -76 ( 5 J mol -1 K -1 ) obtained from the temperature dependence of k 4 are also consistent with gating by protein-protein reorientation (4)(5)(6). Fitting the temperature dependence of k 4 with the Marcus equation (eq 3) gives a reorganization energy λ of 1.9 eV, which is much larger than the value of 0.5-0.9 eV predicted for the elementary electron transfer step in this system (22).…”

Section: Discussionsupporting

confidence: 81%

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Role of Configurational Gating in Intracomplex Electron Transfer from Cytochrome c to the Radical Cation in Cytochrome c Peroxidase

et al. 1999

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Electron transfer within complexes of cytochrome c (Cc) and cytochrome c peroxidase (CcP) was studied to determine whether the reactions are gated by fluctuations in configuration. Electron transfer in the physiological complex of yeast Cc (yCc) and CcP was studied using the Ru-39-Cc derivative, in which the H39C/C102T variant of yeast iso-1-cytochrome c is labeled at the single cysteine residue on the back surface with trisbipyridylruthenium(II). Laser excitation of the 1:1 Ru-39-Cc-CcP compound I complex at low ionic strength results in rapid electron transfer from RuII to heme c FeIII, followed by electron transfer from heme c FeII to the Trp-191 indolyl radical cation with a rate constant keta of 2 x 10(6) s-1 at 20 degrees C. keta is not changed by increasing the viscosity up to 40 cP with glycerol and is independent of temperature. These results suggest that this reaction is not gated by fluctuations in the configuration of the complex, but may represent the elementary electron transfer step. The value of keta is consistent with the efficient pathway for electron transfer in the crystalline yCc-CcP complex, which has a distance of 16 A between the edge of heme c and the Trp-191 indole [Pelletier, H., and Kraut, J. (1992) Science 258, 1748-1755]. Electron transfer in the complex of horse Cc (hCc) and CcP was examined using Ru-27-Cc, in which hCc is labeled with trisbipyridylruthenium(II) at Lys-27. Laser excitation of the Ru-27-Cc-CcP complex results in electron transfer from RuII to heme c FeII with a rate constant k1 of 2.3 x 10(7) s-1, followed by oxidation of the Trp-191 indole to a radical cation by RuIII with a rate constant k3 of 7 x 10(6) s-1. The cycle is completed by electron transfer from heme c FeII to the Trp-191 radical cation with a rate constant k4 of 6.1 x 10(4) s-1. The rate constant k4 decreases to 3.4 x 10(3) s-1 as the viscosity is increased to 84 cP, but the rate constants k1 and k3 remain the same. The results are consistent with a gating mechanism in which the Ru-27-Cc-CcP complex undergoes fluctuations between a major state A with the configuration of the hCc-CcP crystalline complex and a minor state B with the configuration of the yCc-CcP complex. The hCc-CcP complex, state A, has an inefficient pathway for electron transfer from heme c to the Trp-191 indolyl radical cation with a distance of 20.5 A and a predicted value of 5 x 10(2) s-1 for k4A. The observed rate constant k4 is thus gated by the rate constant ka for conversion of state A to state B, where the rate of electron transfer k4B is expected to be 2 x 10(6) s-1. The temperature dependence of k4 provides activation parameters that are consistent with the proposed gating mechanism. These studies provide evidence that configurational gating does not control electron transfer in the physiological yCc-CcP complex, but is required in the nonphysiological hCc-CcP complex.

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Section: Discussionsupporting

confidence: 81%

“…These observations suggest that k eta is not controlled by configurational gating, but may represent the elementary electron transfer event. Previously examined systems in which electron transfer is limited by configurational gating are characterized by a large dependence of the rate constant on viscosity and temperature ( − ).…”

Section: Discussionmentioning

confidence: 99%

Role of Configurational Gating in Intracomplex Electron Transfer from Cytochrome c to the Radical Cation in Cytochrome c Peroxidase

et al. 1999

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“…The high and increasing resin viscosities affect the behavior of the chemical reactions occurring within them. , For instance, in a previous study we found that the high viscosity of the reaction media changed the trend of the ET reactions in thiol–ene polymerization resins by affecting reorganization energies of thiol monomers . Several other studies have also observed viscosity-dependent effects on chemical reactivity. − …”

Section: Resultsmentioning

confidence: 84%

Rational Design of Efficient Amine Reductant Initiators for Amine–Peroxide Redox Polymerization

et al. 2019

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Amine−peroxide redox polymerization (APRP) has been highly prevalent in industrial and medical applications since the 1950s, yet the initiation mechanism of this radical polymerization process is poorly understood so that innovations in the field are largely empirically driven and incremental. Through a combination of computational prediction and experimental analysis, we elucidate the mechanism of this important redox reaction between amines and benzoyl peroxide for the ambient production of initiating radicals. Our calculations show that APRP proceeds through S N 2 attack by the amine on the peroxide but that homolysis of the resulting intermediate is the rate-determining step. We demonstrate a correlation between the computationally predicted initiating rate and the experimentally measured polymerization rate with an R 2 = 0.80. The new mechanistic understanding was then applied to computationally predict amine reductant initiators with faster initiating kinetics. This led to our discovery of N-(4-methoxyphenyl)pyrrolidine (MPP) as amine reductant, which we confirmed significantly outperforms current state-of-the-art tertiary aromatic amines by ∼20-fold, making it the most efficient amine−peroxide redox initiator to date. The application of amines with superior kinetics such as MPP in APRP could greatly accelerate existing industrial processes, facilitate new industrial manufacturing methods, and improve biocompatibility in biomedical applications conducted with reduced initiator concentrations yet higher overall efficiency.

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“…The isokinetic correlation, which holds well for the aforementioned unimolecular reactions, does not apply to the redox reaction between ferrocytochrome c and cupriplastocyanin. Activation parameters ∆H q and ∆S q were reported in studies in which this reaction was induced by mixing (39) and by intramolecular reduction of ferricytochrome c by a ruthenium(II) complex attached to the surface of this protein (98). The former reaction, between the native proteins, is certainly bimolecular.…”

Section: Choice Of Mutations Is Guided By Previous Experimentsmentioning

confidence: 99%

Effects of Single and Double Mutations in Plastocyanin on the Rate Constant and Activation Parameters for the Rearrangement Gating the Electron-Transfer Reaction between the Triplet State of Zinc Cytochromecand Cupriplastocyanin

et al. 1998

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The unimolecular rate constant for the photoinduced electron-transfer reaction 3Zncyt/pc(II) --> Zncyt+/pc(I) within the electrostatic complex of zinc cytochrome c and spinach cupriplastocyanin is kF. We report the effects on kF of the following factors, all at pH 7.0: 12 single mutations on the plastocyanin surface (Leu12Asn, Leu12Glu, Leu12Lys, Asp42Asn, Asp42Lys, Glu43Asn, Glu59Gln, Glu59Lys, Glu60Gln, Glu60Lys, Gln88Glu, and Gln88Lys), the double mutation Glu59Lys/Glu60Gln, temperature (in the range 273.3-302.9 K), and solution viscosity (in the range 1. 00-116.0 cP) at 283.2 and 293.2 K. We also report the effects of the plastocyanin mutations on the association constant (Ka) and the corresponding free energy of association (DeltaGa) with zinc cytochrome c at 298.2 K. Dependence of kF on temperature yielded the activation parameters DeltaH, DeltaS, and DeltaG. Dependence of kF on solution viscosity yielded the protein friction and confirmed the DeltaG values determined from the temperature dependence. The aforementioned intracomplex reaction is not a simple electron-transfer reaction because donor-acceptor electronic coupling (HAB) and reorganizational energy (lambda), obtained by fitting of the temperature dependence of kF to the Marcus equation, deviate from the expectations based on precedents and because kF greatly depends on viscosity. This last dependence and the fact that certain mutations affect Ka but not kF are two lines of evidence against the mechanism in which the electron-transfer step is coupled with the faster, but thermodynamically unfavorable, rearrangement step. The electron-transfer reaction is gated by the slower, and thus rate determining, structural rearrangement of the diprotein complex; the rate constant kF corresponds to this rearrangement. Isokinetic correlation of DeltaH and DeltaS parameters and Coulombic energies of the various configurations of the Zncyt/pc(II) complex consistently show that the rearrangement is a facile configurational fluctuation of the associated proteins, qualitatively the same process regardless of the mutations in plastocyanin. Correlation of kF with the orientation of the cupriplastocyanin dipole moment indicates that the reactive configuration of the diprotein complex involves the area near the residue 59, between the upper acidic cluster and the hydrophobic patch. Kinetic effects and noneffects of plastocyanin mutations show that the rearrangement from the initial (docking) configuration, which involves both acidic clusters, to the reactive configuration does not involve the lower acidic cluster and the hydrophobic patch but involves the upper acidic cluster and the area near the residue 88.

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Temperature and viscosity dependence of the electron-transfer reaction between plastocyanin and cytochrome c labeled with a ruthenium(II) bipyridine complex

Cited by 17 publications

References 8 publications

Role of Configurational Gating in Intracomplex Electron Transfer from Cytochrome c to the Radical Cation in Cytochrome c Peroxidase

Role of Configurational Gating in Intracomplex Electron Transfer from Cytochrome c to the Radical Cation in Cytochrome c Peroxidase

Rational Design of Efficient Amine Reductant Initiators for Amine–Peroxide Redox Polymerization

Effects of Single and Double Mutations in Plastocyanin on the Rate Constant and Activation Parameters for the Rearrangement Gating the Electron-Transfer Reaction between the Triplet State of Zinc Cytochromecand Cupriplastocyanin

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