共查询到20条相似文献,搜索用时 9 毫秒
1.
2.
Isabel B. Coutinho David L. Turner Ming Y. Liu Jean LeGall António V. Xavier 《Journal of biological inorganic chemistry》1996,1(4):305-311
The trihaem cytochrome c
551.5, formerly known as cytochrome c
7, from the organism Desulfuromonas
acetoxidans, has been studied in the reduced state by 2D proton NMR. The haem proton resonances were assigned, and several nuclear Overhauser
enhancements (NOEs) between resonances arising from different haems were detected and assigned. The relative orientations
of the three haems were calculated by fitting both the intensities of the interhaem NOEs and the magnitudes of the ring current
shifts of the haem resonances, following the strategy previously used by the authors to reassess the X-ray structure of the
haem core in tetrahaem cytochrome c
3 from Desulfumicrobium baculatum.
It is concluded that, although the comparison of the protein sequence with those of the tetrahaem cytochromes c
3 shows that in cytochrome c
551.5 about 40% of the sequence is deleted, including the region involved in the attachment of the second of the four haems, this
does not induce any significant rearrangement of the remaining three haems other than a slight decrease in the iron-iron distance
between two of the haems, namely those corresponding to haems I and IV of cytochrome c
3.
Received: 2 February 1996 / Accepted: 26 March 1996 相似文献
3.
P. J. Martel Cláudio M. Soares António M. Baptista M. Fuxreiter Gábor Náray-Szabó Ricardo O. Louro Maria A. Carrondo 《Journal of biological inorganic chemistry》1999,4(1):73-86
A comparative study of the pH-dependent redox mechanisms of several members of the cytochrome c
3 family has been carried out. In a previous work, the molecular determinants of this dependency (the so-called redox-Bohr
effect) were investigated for one species using continuum electrostatic methods to find groups with a titrating range and
strength of interaction compatible with a mediating role in the redox-Bohr effect. Here we clarify these aspects in the light
of new and improved pK
a calculations, our findings supporting the hypothesis of propionate D from heme I being the main effector in the pH-dependent
modulation of the cytochrome c
3 redox potentials in all the c
3 molecules studied here. However, the weaker (but significant) role of other titrating groups cannot be excluded, their importance
and identity changing with the particular molecule under study. We also calculate the relative redox potentials of the four
heme centers among the selected members of the c
3 family, using a continuum electrostatic method that takes into account both solvation and interaction effects. Comparison
of the calculated values with available data for the microscopic redox potentials was undertaken, the quality of the agreement
being dependent upon the choice of the dielectric constant for the protein interior. We find that high dielectric constants
give best correlations, while low values result in better magnitudes for the calculated potentials. The possibility that the
crystallographic calcium ion in c
3 from Desulfovibrio gigas may be present in the solution structure was tested, and found to be likely.
Received: 31 August 1998 / Accepted: 20 November 1998 相似文献
4.
Roberto P. Christen Spyros I. Nomikos E. T. Smith 《Journal of biological inorganic chemistry》1996,1(6):515-522
The change in the equilibrium reduction potentials of the iron-sulfur proteins, Pyrococcus furiosus rubredoxin and P. furiosus ferredoxin, and heme protein, horse cytochrome c, has been calculated as a function of temperature using a numerical solution to the Poisson-Boltzman equation. Working curves
for different internal dielectric constants were generated to best reproduce experimental observation. Based on a comparison
of the experimental and simulated change in reduction potential with temperature, it is concluded that the dielectric constant
of proteins is temperature-dependent and varies from protein to protein. For example, the temperature-dependent reduction
potential of cytochrome c can only be simulated using a different temperature-dependent dielectric constant for each oxidation state, but this was
not the case for rubredoxin or ferredoxin. The role of changes in ionization states of cytochrome c at alkaline pHs, where the reduction potential is known to be pH-dependent at room temperature, is also discussed in terms
of electrostatic interaction energies as a function of temperature. It appears that temperature/reduction potential profiles
may provide a direct method for measuring relative changes in internal protein dielectric constants.
Received: 29 April 1996 / Accepted: 1 August 1996 相似文献
5.
Several cytochromes c2 from the Rhodospirillaceae show a pH dependence of redox potential in the physiological pH range which can be described by equations involving an ionisation in the oxidised form (pKo) and one in the reduced form (pKr). These cytochromes fall into one of two groups according to the degree of separation of pKo and pKr. In group A, represented here by the Rhodomicrobium vannielii cytochrome c2, the separation is approx. one pH unit and the ionisation is that of a haem propionic acid. Members of this group are unique among both cytochromes c2 and mitochondrial cytochromes c in lacking the conserved residue Arg-38. We propose that the role of Arg-38 is to lower the pK of the nearby propionic acid, so that it lies out of the physiological pH range. Substitution of this residue by an uncharged amino acid leads to a raised pK for the propionic acid. In group B, represented here by Rhodopseudomonas viridis cytochrome c2, the separation between pKo and pKr is approx. 0.4 pH unit and the ionisable group is a histidine at position 39. This was established by NMR spectroscopy and confirmed by chemical modification. Only a few other members of the cytochrome c2/mitochondrial cytochrome c family have a histidine at this position and of these, both Crithidia cytochrome c-557 and yeast cytochrome c were found to have a pH-dependent redox potential similar to that of Rps. viridis cytochrome c2. Using Coulomb's law, it was found that the energy required to separate pKo and pKr could be accounted for by simple electrostatic interactions between the haem iron and the ionisable group. 相似文献
6.
Artemiza S. Morar Dionysios Kakouras Gregory B. Young Jonathan Boyd G. J. Pielak 《Journal of biological inorganic chemistry》1999,4(2):220-222
We present a simple and inexpensive method for producing 15N-labeled Saccharomyces cerevisiae
iso-1-cytochrome c in Escherichia coli. The labeled protein gives excellent NMR spectra.
Received: 18 December 1998 / Accepted: 27 January 1999 相似文献
7.
Lucia Banci I. Bertini G. Quacquarini Olaf Walter Antonio Díaz Manuel Hervás Miguel A. de la Rosa 《Journal of biological inorganic chemistry》1996,1(4):330-340
The three-dimensional structure in solution of the reduced form of cytochrome c
6 from the green alga Monoraphidium braunii has been solved through NMR data. Cytochrome c
6 acts as a small mono-heme electron carrier protein between the two membrane-embedded complexes cytochrome f and photosystem I. The structure was determined using 1278 relevant interproton NOEs out of 1776 assigned NOEs with distance
geometry (DG) calculations which included 36 stereospecific assignments and 20 experimentally found angle constraints. The
family of structures obtained from the DG calculations was subjected to energy minimization and molecular dynamics simulation
using previously defined force field parameters for the heme and its ligands. In all stages of the calculations, the solution
structure is well defined and similar to the now available X-ray structure.
Received: 18 January 1996 / Accepted: 19 April 1996 相似文献
8.
Milagros Medina Ricardo O. Louro Jean Gagnon Maria Luisa Peleato Joaquim Mendes Carlos Gómez-Moreno António V. Xavier M. Teixeira 《Journal of biological inorganic chemistry》1997,2(2):225-234
A soluble monoheme c–type cytochrome c
6 has been isolated from the cyanobacterium Anabaena PCC 7119. It is a basic protein, with a molecular mass of 9.7 kDa, which accepts electrons from Anabaena ferredoxin in the ferredoxin-NADP+reductase-dependent NADPH cytochrome c reductase activity assay. The turnover of the reaction has an optimum pH at 7.5. Flavodoxin can also replace ferredoxin in
this assay, but with only 20% efficiency. Plastocyanin from Anabaena PCC 7119, as well as the c
6 cytochromes from the green algae Chlorella fusca and Monoraphidium braunii are also shown to accept electrons from Anabaena ferredoxin. The reduction potential of cytochrome c
6 at pH 6.7 was determined to be 338 mV and is pH dependent, with pK
a
ox=8.4±0.1 and pK
a
red≈9.5. The ferric and ferrous cytochrome forms and their pH equilibria have been studied using visible, EPR and 1H-NMR spectroscopies. The amino acid sequence and the visible and NMR spectroscopic data indicate that the heme iron has a
methionine-histidine axial coordination in the pH range 5–11. However, the EPR data for the ferricytochrome are complex and
show that in this pH range five distinct forms are present. Between pH 5 and 9 the spectrum is dominated by two rhombic species,
with g–values at 2.94, 2.29, 1.43 and at 2.84, 2.34, 1.56, which interconvert with a pK
a of 8.4. The NMR data also show a main interconversion between two cytochrome forms at this pH, which coincides with that
determined from the pH dependence of the reduction potential. Both these forms were associated with a methionine-histidine
heme-iron coordination by correlation with the visible and NMR spectral data, although having crystal field parameters atypical
for this type of coordination. Anabaena cytochrome c
6 is one more example of a heme protein for which the widely used crystal field analysis of the EPR data (truth diagram) fails
to unequivocally determine the type of heme-iron ligation.
Received: 17 May 1996 / Accepted: 13 January 1997 相似文献
9.
Duncan M. Short Malcolm D. Walkinshaw Paul Taylor Graeme A. Reid S. K. Chapman 《Journal of biological inorganic chemistry》1998,3(3):246-252
Saccharomyces cerevisiae flavocytochrome b 2 couples the oxidation of L-lactate to the reduction of cytochrome c. The second-order rate constant for cytochrome c reduction by flavocytochrome b 2 depends on the rate of complex formation and is sensitive to ionic strength. Mutations in the heme domain of flavocytochrome b 2 (Glu63→Lys, Asp72→Lys and the double mutation Glu63→Lys:Asp72→Lys) have significant effects on the reaction with cytochrome c, implicating these residues in complex formation. This kinetic information has been used to guide molecular modelling studies, which are consistent with there being no one single best-configuration. Rather, there is a set of possible complexes in which the docking-face of cytochrome c can approach flavocytochrome b 2 in a variety of orientations. Four cytochromes c can be accommodated on the flavocytochrome b 2 tetramer, with each cytochrome c forming interactions with only one flavocytochrome b 2 subunit. All the models involve residues 72 and 63 on flavocytochrome b 2 but in addition predict that Glu237 may also be important for complex formation. These acidic residues interact with the basic residues 13, 27 and 79 on cytochrome c. Through this triangle of interactions runs a possible σ-tunnelling pathway for electron transfer. This pathway starts with the imidazole ring of His66 (a ligand to the heme-iron of flavocytochrome b 2) and ends with the ring of Pro68, which is in van der Waals contact with the cytochrome c heme. In total, the edge-to-edge "through space" distance from the imidazole ring of His66 to the C3C pyrrole ring of cytochrome c is 13.1?Å. 相似文献
10.
Helder Lopes Graham W. Pettigrew Isabel Moura José J. G. Moura 《Journal of biological inorganic chemistry》1998,3(6):632-642
The di-haem cytochrome c peroxidase of Paracoccus denitrificans is a calcium binding dimer of 37.5 kDa subunits. It is responsible for reduction of H2O2 to H2O with oxidation of cytochrome c
550 and is isolated in a fully oxidised state (inactive) in which one haem (centre I) is in a high-spin/low-spin equilibrium
and high potential and the other (centre II) is low-spin and low potential. The enzyme undergoes direct electron transfer
(without the need for mediators) with a 4,4′-dithiodipyridine-modified gold electrode and the response of both haem groups
can be observed. By combination of the cyclic and pulse voltammetric data with the established spectroscopic information,
it was demonstrated that entry of one electron to the high potential haem leads (in a mechanism involving strong haem-haem
interactions) to a complex change of spin states and redox potentials of both haems in order to attain a "ready state" for
binding, reduction and cleavage of the hydrogen peroxide. In the absence of endogenous calcium, haem communication can be
completely disconnected and is recovered only when Ca2+ is added, an essential step for the formation of the peroxidatic site. The intricate electrochemical behaviour of this enzyme
was interpreted as a mechanism involving, both reduction and oxidation of the high potential haem, an interfacial electron
transfer coupled to a homogenous chemical reaction (EC mechanism). We discuss two different models for the sequence of events
leading to the appearance of the active pentacoordinated peroxidatic haem.
Received: 29 April 1998 / Accepted: 3 September 1998 相似文献
11.
Mikkel Nissum Jens-Jakob Karlsson Jens Ulstrup Palle Waage Jensen G. Smulevich 《Journal of biological inorganic chemistry》1997,2(3):302-307
Di-heme Pseudomonas stutzeri cytochrome c
4 has been characterized by electronic absorption and resonance Raman spectroscopies in the ferric and ferrous forms at pH 7.5
and at room temperature. The data indicate that the two hemes are inequivalent. It is proposed that the N-terminal contains
a more relaxed heme as a consequence of the relative orientation of the methionine and histidine ligands with respect to the
N-Fe-N directions of the heme plane. This causes a weakening of the Fe-S bond with concomitant partial dissociation of the
methionine and the formation of an Fe-aquo bond. Heme group relaxation is further accompanied by less distortion of the heme
group than that associated with cytochrome c, expansion of the "core" and a negative shift of the redox potential.
Received: 17 December 1996 / Accepted: 6 March 1997 相似文献
12.
Cláudio M. Soares Paulo J. Martel Maria A. Carrondo 《Journal of biological inorganic chemistry》1997,2(6):714-727
The pH dependence of the redox potentials in the tetrahemic cytochrome c
3 from Desulfovibrio vulgaris Hildenborough (redox-Bohr effect) is here investigated using continuum electrostatics methods. The redox-Bohr effect seems
to be associated with changes in the protonation state of charged residues in the protein, but the exact residues had not
been identified. The global pK
a of this phenomenon is dependent on the redox state of the molecule, and the influence of the pH on the microscopic potential
of each heme has been experimentally quantified. The availability of detailed experimental data provides us with important
and unique guides to the performance of ab initio pK
a calculations aiming at the identification of the groups involved. These calculations were performed in several redox states
along the reduction pathway, with the double objective of finding groups with redox-linked pK
a shifts, and absolute pK
as compatible with the redox-Bohr effect. The group with the largest pK
a shift along the reduction pathway is propionate D from heme I. Its effect on the redox potential of individual hemes, as
calculated by electrostatic calculations, correlates very well with the experimental order of influence, making it a likely
candidate. Abnormal titration of the same propionate has been experimentally observed on a homologous cytochrome c
3 from a different strain, thus strengthening the theoretical result. However, its absolute calculated pK
a in the fully oxidised cytochrome is outside the zone where the phenomenon is known to occur, but the calculation shows a
strong dependence on small conformational changes, suggesting large uncertainties in the calculated value. A group with a
pK
a value within the experimentally observed range is propionate D from heme IV. Its influence on the redox potential of the
hemes does not correlate with the experimental order, indicating that, although it may be one of the possible players on the
phenomenon, it cannot be solely responsible for it. Mutation of the Lys45 residue is suggested as an indirect way of probing
the importance of the propionate D from heme I in the mechanism. Non-heme groups may also be involved in this process; our
calculations indicate His67 and the N-terminal as groups that may play a role. Accuracy and applicability of current continuum
electrostatic methods are discussed in the context of this system.
Received: 27 March 1997 / Accepted: 19 August 1997 相似文献
13.
Kagan VE Borisenko GG Tyurina YY Tyurin VA Jiang J Potapovich AI Kini V Amoscato AA Fujii Y 《Free radical biology & medicine》2004,37(12):1963-1985
The primary life-supporting function of cytochrome c (cyt c) is control of cellular energetic metabolism as a mobile shuttle in the electron transport chain of mitochondria. Recently, cyt c's equally important life-terminating function as a trigger and regulator of apoptosis was identified. This dreadful role is realized through the relocalization of mitochondrial cyt c to the cytoplasm where it interacts with Apaf-1 in forming apoptosomes and mediating caspase-9 activation. Although the presence of heme moiety of cyt c is essential for the latter function, cyt c's redox catalytic features are not required. Lately, two other essential functions of cyt c in apoptosis, that may rely heavily on its redox activity have been suggested. Both functions are directed toward oxidation of two negatively charged phospholipids, cardiolipin (CL) in the mitochondria and phosphatidylserine (PS) in the plasma membrane. In both cases, oxidized phospholipids seem to be essential for the transduction of two distinctive apoptotic signals: one is participation of oxidized CL in the formation of the mitochondrial permeability transition pore that facilitates release of cyt c into the cytosol and the other is the contribution of oxidized PS to the externalization and recognition of PS (and possibly oxidized PS) on the cell surface by specialized receptors of phagocytes. In this review, we present a new concept that cyt c actuates both of these oxidative roles through a uniform mechanism: its specific interactions with each of these phospholipids result in the conversion and activation of cyt c, transforming it from an innocuous electron transporter into a calamitous peroxidase capable of oxidizing the activating phospholipids. We also show that this new concept is compatible with a leading role for reactive oxygen species in the execution of the apoptotic program, with cyt c as the main executioner. 相似文献
14.
Giampiero De Sanctis Alessandra Maranesi Tommaso Ferri Alessandro Poscia Franca Ascoli Roberto Santucci 《Journal of Protein Chemistry》1996,15(7):599-606
The effect of glycerol on the structure and redox properties of horse heart cytochrome c was investigated by absorption spectroscopy, circular dichroism, and dc cyclic voltammetry techniques. The results show that the organic solvent increases the -helix structure of the protein and induces slight changes at the active-site environment; however, the overall tertiary structure does not appear to be significantly perturbed. Glycerol stabilizes cytochrome c, the free energy of denaturation (G
0) being approximately 0.7 kcal/mol larger than that determined in phosphate buffer under the same conditions, and influences the heterogeneous electron transfer kinetics at a chemically modified gold electrode; on the other hand, the redox potential of the protein is unaltered. On the whole, the results obtained indicate that glycerol acts as a suitable stabilizing agent of cytochrome c, which is of interest for application in biotechnology; the organic solvent does not alter the tertiary structure significantly or the redox properties of the protein. This has to be interpreted not only in terms of the glycerol-induced solvent ordering around the protein surface, but also as due to the specific features of the protein matrix. 相似文献
15.
Huan-Xiang Zhou 《Journal of biological inorganic chemistry》1997,2(1):109-113
Factors that contribute to the control of reduction potential by protein matrix are examined within a spherical protein model.
These include the nonpolar nature of protein matrices, solvent accessibility of the redox center, and net charges and dipoles
of surrounding amino acids. Simple rules on their effects are established. In particular, surface charges have little effect
on the reduction potential, and polar groups may either increase or decrease the reduction potential, depending on their orientations
relative to the redox center. The effects of complex formation, proton titration, and ionic strength are also discussed.
Received, accepted: 26 November 1996 相似文献
16.
G R Moore 《FEBS letters》1983,161(2):171-175
An assessment is made of the proposal: electrostatic interactions between the ferric ion of oxidised cytochrome c and its haem propionate sidechains assists in determining the value of the redox potential and plays an important role in the redox state conformation change. Differences between the properties of homologous cytochromes are proposed to be due to differences associated with the charge on their haem propionates. 相似文献
17.
Johan Leckner Pernilla Wittung Nicklas Bonander B. G. Karlsson Bo G. Malmström 《Journal of biological inorganic chemistry》1997,2(3):368-371
The unfolding of oxidized and reduced azurin by guanidine hydrochloride has been monitored by circular dichroism. Dilution
experiments showed the unfolding to be reversible, and the equilibrium data have been interpreted in terms of a two-state
model. The protein is stabilized by the strong metal binding in the native state, so that the folding free energy is as high
as –52.2 kJ mol–1 for the oxidized protein. The reduced protein is less stable, with a folding free energy of –40.0 kJ mol–1. A thermodynamic cycle shows, as a consequence, that unfolded azurin has a reduction potential 0.13 V above that of the folded
protein. This is explained by the bipyramidal site in the native fold stabilizing Cu(II) by a rack mechanism, with the same
geometry being maintained in the Cu(I) form. In the unfolded protein, on the other hand, the coordination geometries are expected
to differ for the two oxidation states, Cu(I) being stabilized by the cysteine thiol group in a linear or trigonal symmetry,
whereas Cu(II) prefers oxygen ligands in a tetragonal geometry.
Received: 15 January 1997 / Accepted: 3 April 1997 相似文献
18.
19.
Ricardo O. Louro Teresa Catarino Jean LeGall António V. Xavier 《Journal of biological inorganic chemistry》1997,2(4):488-491
A central step in the metabolism of Desulfovibrio spp. is the oxidation of molecular hydrogen catalyzed by a periplasmic hydrogenase. However, this enzymatic activity is quite
low at physiological pH. The hypothesis that, in the presence of the tetrahaem cytochrome c
3, hydrogenase can maintain full activity at physiological pH through the concerted capture of the resulting electrons and
protons by the cytochrome was tested for the case of Desulfovibrio vulgaris (Hildenborough). The crucial step involves an electron-to-proton energy transduction, and is achieved through a network of
cooperativities between redox and ionizable centers within the cytochrome (redox-Bohr effect). This mechanism, which requires
a relocation of the proposed proton channel in the hydrogenase structure, is similar to that proposed for the transmembrane
proton pumps, and is the first example which shows evidence of functional energy transduction in the absence of a membrane
confinement.
Received: 2 April 1997 / Accepted: 23 May 1997 相似文献
20.
F J Mofers P J Veltkamp E E Van Faassen G Casteleijn Y K Levine 《Biophysical chemistry》1982,16(1):19-25
In this paper, the results are presented of measurements of the dielectric dispersions of horse heart cytochrome c molecules in various buffers. The data are fitted to the Cole-Cole relaxation model. The influence of the concentration and the ionic strength on the parameters that result from the Cole-Cole model is determined. The measured data are compared with calculations based on the model presented previously. Good agreement is found between the model and the observed data. 相似文献