Long range electron transfer between tyrosine and tryptophan in hen egg-white lysozyme

Weinstein, M.; Alfassi, Zeev B.; DeFelippis, Michael R.; Klapper, Michael H.; Faraggi, M.

doi:10.1016/0167-4838(91)90262-x

Cited by 56 publications

(37 citation statements)

References 34 publications

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“…However, considering that protein radicals are so easily found in peroxidase mimics such as myoglobin and cytochrome c (see above), it is possible that guaiacol is oxidized via one of these radicals. Unstabilized protein radicals can be transferred easily and rapidly between different sites on a protein [51–54], and thus also to the two surface exposed tyrosines of cytochrome c‐ 550 [16,17], which might be involved in guaiacol oxidation. Studies on the myoglobin/H 2 O 2 catalysed oxygenation and oxidation reactions provide evidence that a protein radical is indeed the true oxidizing species in such types of reactions [54–61].…”

Section: Discussionmentioning

confidence: 99%

The peroxidase activity of cytochrome c‐550 from Paracoccus versutus

Diederix¹,

Ubbink²,

Canters³

2001

European Journal of Biochemistry

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Next to their natural electron transport capacities, c-type cytochromes possess low peroxidase and cytochrome P-450 activities in the presence of hydrogen peroxide. These catalytic properties, in combination with their structural robustness and covalently bound cofactor make cytochromes c potentially useful peroxidase mimics. This study reports on the peroxidase activity of cytochrome c-550 from Paracoccus versutus and the loss of this activity in presence of H 2 O 2 . The rate-determining step in the peroxidase reaction of cytochrome c-550 is the formation of a reactive intermediate, following binding of peroxide to the haem iron. The reaction rate is very low compared to horseradish peroxidase (approximately one millionth), because of the poor accessibility of the haem iron for H 2 O 2 , and the lack of a base catalyst such as the distal His of the peroxidases. This is corroborated by the linear dependence of the reaction rate on the peroxide concentration up to at least 1 m H 2 O 2 . Steady-state conversion of a reducing substrate, guaiacol, is preceded by an activation phase, which is ascribed to the build-up of amino-acid radicals on the protein. The inactivation kinetics in the absence of reducing substrate are mono-exponential and shown to be concurrent with haem degradation up to 25 mm H 2 O 2 (pH 8.0). At still higher peroxide concentrations, inactivation kinetics are biphasic, as a result of a remarkable protective effect of H 2 O 2 , involving the formation of superoxide and ferrocytochrome c-550.Keywords: cytochrome c; peroxidase; protein radicals; haem; oxidation.Peroxidases are haem containing enzymes that efficiently catalyse substrate oxidations using hydrogen peroxide [1,2]. Peroxidases can function as catalysts in a variety of oxidation reactions on a broad spectrum of substrates and their potential use is therefore considerable. This is more so because they utilize the`clean' oxidant H 2 O 2 [2]. Unfortunately, peroxidases are prone to inactivation during normal turnover. This inherent instability is poorly understood and it is important to investigate the mechanism of inactivation because it is currently the main restriction to commercial application of peroxidases and peroxidase mimics [2±4].Peroxidase activity is inherent to many haem-proteins besides peroxidases. It has been detected in, e.g. haemoglobins and myoglobins, cytochrome c and microperoxidases [5±10]. The latter are small peptides derived from extensive proteolysis of cytochrome c, which have contained a covalently bound haem moiety [8,11]. In some cases protein modification has resulted in enhanced activity [12±14]. Understanding the peroxidase properties of c-type cytochromes is particularly interesting, because these are very stable proteins that remain highly soluble even under conditions of extreme heat, acidity and basicity. Importantly, the covalent linkage, via thioether bonds, of their haem prosthetic group to the protein matrix prevents dissociation of the catalytic moiety from the protein. These properties render cyto...

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Section: Discussionmentioning

confidence: 99%

The peroxidase activity of cytochrome c‐550 from Paracoccus versutus

Diederix¹,

Ubbink²,

Canters³

2001

European Journal of Biochemistry

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“…Thus, if the fluorescence decay of RNT1 is monoexponential at pH 5.5 (James et al 1985) and biexponential at pH 7.4 (Table 1), it seems plausible that the change in ET rate with pH could be concerned. In studies of long‐distance ET in peptide models and proteins, it has been shown that at pH < 6, the ET rate increases (Weinstein et al 1991; Bobrowski et al 1997). Additionally, in different wild‐type and single‐mutated azurins, a significant increase in ET rate was observed upon decreasing the pH from 8 to 4 (Farver et al 1996b).…”

Section: Discussionmentioning

confidence: 99%

On the involvement of electron transfer reactions in the fluorescence decay kinetics heterogeneity of proteins

Ababou

Bombarda

2001

Protein Science

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Time-resolved fluorescence study of single tryptophan-containing proteins, nuclease, ribonuclease T1, protein G, glucagon, and mastoparan, has been carried out. Three different methods were used for the analysis of fluorescence decays: the iterative reconvolution method, as reviewed and developed in our laboratory, the maximum entropy method, and the recent method that we called "energy transfer" method. All the proteins show heterogeneous fluorescence kinetics (multiexponential decay). The origin of this heterogeneity is interpreted in terms of current theories of electron transfer process, which treat the electron transfer process as a radiationless transition. The theoretical electron transfer rate was calculated assuming the peptide bond carbonyl as the acceptor site. The good agreement between experimental and theoretical electron-transfer rates leads us to suggest that the electron-transfer process is the principal quenching mechanism of Trp fluorescence in proteins, resulting in heterogeneous fluorescence kinetics. Furthermore, the origin of apparent homogeneous fluorescence kinetics (monoexponential decay) in some proteins also can be explained on the basis of electron-transfer mechanism.

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“…In the range of ∆G°from -10 to -30 kJ, corresponding approximately to 0.1-0.3 eV, in which values of ∆G°for both reactions 1 and 2 in 3-5 could be expected, 11,15,35,39 λ 298 assumes large values weakly dependent on ∆G°(cf. Figure 6).…”

Section: Molecular Dynamics Of H-trp-(pro) 3 -Tyr-ohmentioning

confidence: 98%

Pulse Radiolysis Studies of Intramolecular Electron Transfer in Model Peptides and Proteins. 8. Trp[NH^•+] → Tyr[O^•] Radical Transformation in H-Trp-(Pro)_n-Tyr-OH, n = 3−5, Series of Peptides

et al. 1999

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The kinetics of intramolecular long-range electron transfer (LRET) between the protonated tryptophan indolyl radical cation Trp[NH •+ ], remaining in equilibrium with its neutral Trp[N • ] form, and tyrosine in aqueous H-Trp-(Pro) n -Tyr-OH, n ) 3-5, peptides (abbreviated 3, 4, and 5) has been studied by pulse radiolysis at pH 2-8 at 298 K and at pH 4 over the temperature range 283-328 K. LRET has been found to occur down to pH 2, contrary to expectations based on the electrochemical redox potentials for Trp and Tyr in the form of free amino acids. The first-order rate constants of LRET, k obs , varied sigmoidally with pH, allowing evaluation of pK a1 's for deprotonation of Trp[NH •+ ]: 3.7, 4.1, and 4.3 for 3, 4, and 5, respectively, as well as the intrinsic rate constants, k 2 , of LRET involving solely Trp[NH •+ ] radicals. Variation of pK a1 was attributed to electrostatic interactions between the indolyl radical and the COOH group of terminal Tyr, expected to decrease in the shown order, and taken as an indication of variation, in the same order, of the electrochemical driving force ∆G°of LRET. In 4 and 5, k 2 proved to be about 60-fold larger than the corresponding k 1 values characteristic for Trp[N • ], which indicates that the kinetics of LRET involving Trp[NH •+ ] exhibits similar through-bond distance dependence as that found earlier for the reaction with Trp[N • ]. For 3 the ratio of k 2 /k 1 was found to be about 3-fold lower than for its two longer-bridged analogues, 4 and 5. Arrhenius activation energies, E a2 , of LRET involving Trp[NH •+ ] proved to be rather low for 4 and 5, 8.6 and 7.2 kJ mol -1 , respectively. In the case of 3, however, k obs varied nonlinearly with temperature. A nonlinear fit of Arrhenius type function to k obs (T) data under the assumption δE a2 /δT ) 0 and δpK a1 /δT * 0 gave E a2 of 31.6 kJ mol -1 and indicated a decrease in pK a1 of Trp[NH •+ ] by about one unit in the studied temperature range. Conformational preferences of 3 were thus studied by means of molecular dynamics modeling to understand why the parameters of LRET in this peptide were so different from those of 4 and 5. It has been shown that a f R transition at the central ψ(Pro 3 ) dihedral angle, which could bring NH (indole) and COOH groups into a close contact compatible with formation of a hydrogen bond, may occur in 3 on the time scale of the observed electron-transfer reaction. In longer-bridged analogues two such concerted transitions would be necessary to perturb LRET measurably, an event of extremely low probability. It is thus argued that this transition may explain the kinetic and energetic peculiarities of LRET in 3. Analysis of thermodynamic parameters indicated that in reactions involving both Trp[NH •+ ] as well as Trp[N • ] radicals the free energy barrier of activation of LRET, ∆G # , is for the most part entropic in nature. A more detailed analysis of thermodynamics of these reactions must await experimental determination of ∆G°for both reactions in the peptides studied.

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Long range electron transfer between tyrosine and tryptophan in hen egg-white lysozyme

Cited by 56 publications

References 34 publications

The peroxidase activity of cytochrome c‐550 from Paracoccus versutus

The peroxidase activity of cytochrome c‐550 from Paracoccus versutus

On the involvement of electron transfer reactions in the fluorescence decay kinetics heterogeneity of proteins

Pulse Radiolysis Studies of Intramolecular Electron Transfer in Model Peptides and Proteins. 8. Trp[NH^•+] → Tyr[O^•] Radical Transformation in H-Trp-(Pro)_n-Tyr-OH, n = 3−5, Series of Peptides

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Long range electron transfer between tyrosine and tryptophan in hen egg-white lysozyme

Cited by 56 publications

References 34 publications

The peroxidase activity of cytochrome c‐550 from Paracoccus versutus

The peroxidase activity of cytochrome c‐550 from Paracoccus versutus

On the involvement of electron transfer reactions in the fluorescence decay kinetics heterogeneity of proteins

Pulse Radiolysis Studies of Intramolecular Electron Transfer in Model Peptides and Proteins. 8. Trp[NH•+] → Tyr[O•] Radical Transformation in H-Trp-(Pro)n-Tyr-OH, n = 3−5, Series of Peptides

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Pulse Radiolysis Studies of Intramolecular Electron Transfer in Model Peptides and Proteins. 8. Trp[NH^•+] → Tyr[O^•] Radical Transformation in H-Trp-(Pro)_n-Tyr-OH, n = 3−5, Series of Peptides