Species specificity of long-range electron transfer within the complex between zinc-substituted cytochrome c peroxidase and cytochrome c

Ho, P Shing; Sutoris, Carol; Liang, Nong; Margoliash, E.; Hoffman, Brian M.

doi:10.1021/ja00290a059

Cited by 68 publications

(64 citation statements)

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“…In 100 mM KPi conditions, addition of Fe(III)Cc in twofold excess increases the rate constant for triplet state decay to k P = ( k D + k e ) = 230 ± 12 s −1 (Table 2 and Figure 7). The increased quenching primarily results from ET to Fe(III)Cc 14, 15, 32 ( k e = k P – k D = 116 s −1 ), which is consistent with there being little change in rate constant (< 10 s −1 ) when reduced Fe(II)Cc is added. For WT ZnCcP:Cc, the k eb indeed exceeds k e and thus an intermediate state could not be resolved (for individual acquisition times as low as 1 μsec).…”

Section: Resultssupporting

confidence: 69%

Constraints on the Radical Cation Center of Cytochrome c Peroxidase for Electron Transfer from Cytochrome c

et al. 2016

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The tryptophan 191 cation radical of cytochrome c peroxidase (CcP) compound I (Cpd I) mediates long-range electron transfer (ET) to cytochrome c (Cc). Here we test the effects of chemical substitution at the 191 position. CcP W191Y forms a stable tyrosyl radical on reaction with peroxide and produces spectral properties similar to that of Cpd I but has low reactivity toward reduced Cc. CcP W191G(or F) variants also have low activity, as do redox ligands that bind within the W191G cavity. Crystal structures of complexes between Cc and CcP W191X (X = Y, F, G), as well as W191G with four bound ligands, reveal similar 1:1 association modes and heme pocket conformations. The ligands display structural disorder in the pocket and do not hydrogen bond to Asp235, as does Trp191. Well-ordered Tyr191 directs its hydroxyl group toward the porphyrin ring, with no basic residue in range of interaction. CcP W191X (X = Y, F, G) variants substituted with zinc-porphyrin (ZnP) undergo photoinduced ET with Cc(III). Their slow charge recombination kinetics that results from loss of the radical center allow resolution of difference spectra for the charge-separated state (ZnP+, Cc(II)). The change from a phenyl moiety at position 191 in W191F to a water-filled cavity in W191G produces much smaller effects on ET rates than the change from Trp to Phe. Low net reactivity of W191Y toward Cc(II) either derives from the inability of ZnP+ or the Fe-CcP ferryl to oxidize Tyr or from a low potential of the resulting neutral Tyr radical.

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Section: Resultssupporting

confidence: 69%

Constraints on the Radical Cation Center of Cytochrome c Peroxidase for Electron Transfer from Cytochrome c

et al. 2016

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“…As the computed values of λ put the complexes with F82S(W) further from the maximum value in the Marcus model, (Table 3, using estimated redox potentials as noted 115,116 ) the predicted rate constants for these mutants are more strongly dependent on λ and ΔG than the F82Y(I) mutants and are thus more sensitive to model-dependent uncertainties associated with the FDPB approach for computing λ.…”

Section: Resultsmentioning

confidence: 98%

Distance-Independent Charge Recombination Kinetics in Cytochrome c–Cytochrome c Peroxidase Complexes: Compensating Changes in the Electronic Coupling and Reorganization Energies

et al. 2013

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Charge recombination rate constants vary no more than three-fold for inter-protein ET in the Zn-substituted wild type (WT) cytochrome c peroxidase (CcP):cytochrome c (Cc) complex and in complexes with four mutants of the Cc protein (i.e., F82S, F82W, F82Y and F82I), despite large differences in the ET distance. Theoretical analysis indicates that charge recombination for all complexes involves a combination of tunneling and hopping via Trp191. For three of the five structures (WT and F82S(W)), the protein favors hopping more than that in the other two structures that have longer heme→ZnP distances (F82Y(I)). Experimentally observed biexponential ET kinetics is explained by the complex locking in alternative coupling pathways, where the acceptor hole state is either primarily localized on ZnP (slow phase) or on Trp191 (fast phase). The large conformational differences between the CcP:Cc interface for the F82Y(I) mutants compared to the WT and F82S(W) complexes are predicted to change the reorganization energies for the CcP:Cc ET reactions because of changes in solvent exposure and inter-protein ET distances. Since the recombination reaction is likely to occur in the inverted Marcus regime, an increased reorganization energy compensates the decreased role for hopping recombination (and the longer transfer distance) in the F82Y(I) mutants. Taken together, coupling pathway and reorganization energy effects for the five protein complexes explains the observed insensitivity of recombination kinetics to donor-acceptor distance and docking pose and also reveals how hopping through aromatic residues can accelerate long-range ET.

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“…Steady-state kinetic studies showed only modest effects of substitution at this position (3), but the enzymic reaction is complex (5), and such studies are imperfect windows on the electron-transfer step because they inevitably convolve bimolecular processes and the intracomplex transfer event. Recently, we have shown that it is possible to study long-range electron transfer (6) within the preformed CytcP-Cytc protein complex by substituting zinc protoporphyrin IX (ZnPor) for heme in cytochrome c peroxidase (7,8). Electron transfer from ZnCytcP to Fe(III)Cytc is initiated by flash photoproduction of the zinc protoporphyrin triplet state (3ZnPor), which can reduce a ferriheme partner with rate constant kt (Fig.…”

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confidence: 99%

Yeast cytochrome c with phenylalanine or tyrosine at position 87 transfers electrons to (zinc cytochrome c peroxidase)+ at a rate ten thousand times that of the serine-87 or glycine-87 variants.

Liang¹,

Pielak²,

Mauk³

et al. 1987

Proc. Natl. Acad. Sci. U.S.A.

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BiophysicsYeast cytochrome c with phenylalanine or tyrosine at position 87 transfers electrons to (zinc cytochrome c peroxidase)+ at a rate ten thousand times that of the serine-87 or glycine-87 variants ABSTRACTOf the many factors known to influence the rate of electron transfer between two metalloproteins, it is particularly difficult to assess the role of the polypeptide matrix intervening between the donor and acceptor sites. To determine whether the phylogenetically conserved Phe-87 of yeast iso-i-

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Species specificity of long-range electron transfer within the complex between zinc-substituted cytochrome c peroxidase and cytochrome c

Cited by 68 publications

References 1 publication

Constraints on the Radical Cation Center of Cytochrome c Peroxidase for Electron Transfer from Cytochrome c

Constraints on the Radical Cation Center of Cytochrome c Peroxidase for Electron Transfer from Cytochrome c

Distance-Independent Charge Recombination Kinetics in Cytochrome c–Cytochrome c Peroxidase Complexes: Compensating Changes in the Electronic Coupling and Reorganization Energies

Yeast cytochrome c with phenylalanine or tyrosine at position 87 transfers electrons to (zinc cytochrome c peroxidase)+ at a rate ten thousand times that of the serine-87 or glycine-87 variants.

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