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Biomedical subjects

R M Davydov

Publications and source records attributed to R M Davydov.

At least 19 recordsLinked to original sources
PubMed2001

Synthesis and spectroscopic studies of non-heme diiron(III) species with a terminal hydroperoxide ligand: models for hemerythrin.

Two compounds, [Fe2(mu-OH)(mu-Ph4DBA)(TMEDA)2(OTf)] (4) and [Fe2(mu-OH)(mu-Ph4DBA)(DPE)2(OTf)] (7), where Ph4DBA(2-) is the dinucleating bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate), have been prepared as synthetic models for the dioxygen-binding non-heme diiron protein hemerythrin (Hr). X-ray crystallography reveals that, in the solid state, these compounds contain the asymmetric coordination environment found at the diiron center in the reduced form of the protein, deoxyHr. Mössbauer spectra of the models (4, delta = 1.21(2), DeltaE(Q) = 2.87(2) mm s(-1); 7, delta(av) = 1.23(1), DeltaE(Qav) = 2.79(1) mm s(-1)) and deoxyHr (delta = 1.19, DeltaE(Q) = 2.81 mm s(-1)) are also in good agreement. Oxygenation of the diiron(II) complexes dissolved in CH2Cl2 containing 3 equiv of N-MeIm (4) or neat EtCN (7) at -78 degrees C affords a red-orange solution with optical bands at 336 nm (7300 M(-1) cm(-1)) and 470 nm (2600 M(-1) cm(-1)) for 4 and at 334 nm (6400 M(-1) cm(-1)) and 484 nm (2350 M(-1) cm(-1)) for 7. These spectra are remarkably similar to that of oxyHr, 330 nm (6800 M(-1) cm(-1)) and 500 nm (2200 M(-1) cm(-1)). The electron paramagnetic resonance (EPR) spectrum of the cryoreduced, mixed-valence dioxygen adduct of 7 displays properties consistent with a (mu-oxo)diiron(II,III) core. An investigation of 7 and its dioxygen-bound adduct by extended X-ray absorption fine structure (EXAFS) spectroscopy indicates that the oxidized species contains a (mu-oxo)diiron(III) core with iron-ligand distances in agreement with those expected for oxide, carboxylate, and amine/hydroperoxide donor atoms. The analogous cobalt complex [Co2(mu-OH)(mu-Ph4DBA)(TMEDA)2(OTf)] (6) was synthesized and structurally characterized, but it was unreactive toward dioxygen.

Crystallography, X-Ray↗
PubMed1999

EPR properties of mixed-valent mu-oxo and mu-hydroxo dinuclear iron complexes produced by radiolytic reduction at 77 K.

Radiolytic reduction at 77 K of oxo/hydroxo-bridged dinuclear iron(III) complexes in frozen solutions forms kinetically stabilized, mixed-valent species in high yields that model the mixed-valent sites of non-heme, diiron proteins. The mixed-valent species trapped at 77 K retain ligation geometry similar to the initial diferric clusters. The shapes of the mixed-valent EPR signals depend strongly on the bridging ligands. Spectra of the Fe(II)OFe(III) species reveal an S = 1/2 ground state with small g-anisotropy as characterized by the uniaxial component (gz-gav/2 < 0.03) observable at temperatures as high as approximately 100 K. In contrast, hydroxo-bridged mixed-valent species are characterized by large g-anisotropy (gz-gav/2 > 0.03) and are observable only below 30 K. Annealing at higher temperatures causes structural relaxation and changes in the EPR characteristics. EPR spectral properties allow the oxo- and hydroxo-bridged, mixed-valent diiron centers to be distinguished from each other and can help characterize the structure of mixed-valent centers in proteins.

Anisotropy↗
PubMed1997

EPR study of the mixed-valent diiron sites in mouse and herpes simplex virus ribonucleotide reductases. Effect of the tyrosyl radical on structure and reactivity of the diferric center.

Reduction of ribonucleotide reductase (EC 1.17.4.1) R2 proteins in a frozen glycerol-buffer solution at 77 K by mobile electrons generated by gamma-irradiation produces EPR-detectable iron sites in mixed-valent Fe(II)/Fe(III) states. The primary EPR signals give information about the ligand arrangement of the diferric form of the iron site, whereas secondary signals observed after annealing of the sample show the effects of structural relaxation. In recombinant metR2 proteins (without free radical) from mouse and herpes virus type 1, the mixed-valent sites trapped at 77 K give rise to axial S = 1/2 EPR spectra with g values in the range 1.79-1.94, observable at temperatures up to 110 K. The spectra are assigned to mu-oxo-bridged dinuclear iron sites. In mouse metR2, the primary EPR spectrum is a mixture of two components. Annealing the R2 samples to 160-170 K transforms the primary EPR signals into rhombic spectra, characterized by gav < 1.8, and observable only below 25 K. These spectra are assigned to partially relaxed forms with a mu-hydroxo bridge, formed by protonation of the oxo bridge. Further annealing at 220 K produces new rhombic EPR spectra, which are closely similar with those observed and found to be stable after chemical reduction at room temperature. The EPR signal of the primary mixed-valent iron site in active mouse R2 protein with a tyrosyl radical also has two components. Both are different from those observed in metR2. In herpes simplex virus type 1 protein R2, one primary mixed-valent component was observed for the met protein. The dose-yield curve for the mixed-valent state in active mouse R2 is sigmoidal in shape, indicating that the tyrosyl radical is reduced by mobile electrons before the iron site. Kinetic experiments on the reduction by dithionite on mouse R2 without and with radical show a significantly enhanced rate for reduction of the iron site in the protein without radical. The results suggest that in active mouse R2 only complete diferric sites with neighboring radicals give rise to the mixed-valent spectra, and that these sites may exist in two structurally distinct forms. The results on the mouse R2 proteins confirm and extend previous results obtained on the Escherichia coli protein R2 showing that the presence of the tyrosyl radical significantly affects not only the structure but also the reactivity of the iron site.

Animals↗
PubMed1986

[Effect of lipids and substrates on the kinetics of binding of ferrocytochrome P-450 to CO].

Using the flash photolysis technique, it was found that the kinetics of recombination of carbon monoxide with ferrocytochrome P-450 LM-2 can be approximated by the sum of three exponents. Incorporation of cytochrome P-450 into liposomes prepared from microsomal lipids leads to the reduction of the number of steps to two as well as to essential changes in rate constants. Addition of type I substrates (Triton N-101, albumin) cause similar changes in the reaction kinetics. NADPH-cytochrome P-450 reductase has no effect on this process. The multistep kinetics of CO recombination with cytochrome P-450 LM-2 may be accounted for by the presence of some protein conformers. The experimental results suggest that the activity and structure of cytochrome P-450 conformers is affected by the lipid microenvironment, type I substrates and Triton N-101.

Animals↗
PubMed1982

PH-jump-induced ADP phosphorylation in mitochondria.

Mitochondria, uncoupled by aging or by freeze-thaw treatment, are able to synthesize ATP from ADP and Pi after a fast increase (but not decrease) in the external pH. The maximal ATP yield (approx. 2.5 ATP molecules/electron-transport chain per pH jump) can be obtained under the following conditions: (1) the pH change during the jump must exceed 0.7 pH units; (2) in the course of this change, the pH of the mitochondrial suspension must cross the pH 8.1-8.3 value. This pH-jump-induced ATP synthesis is completely inhibited by oligomycin.

Adenosine Diphosphate↗
PubMed1979

Spectral properties of nonequilibrium states in cytochrome P-450 formed by reduction at subzero temperatures.

Nonequilibrium conformational states in cytochrome P-450 in the presence and absence of substrates formed by reduction at subzero temperatures with hydrates electrons were obtained and characterized by their absorption spectra. Different absorption spectra between the relaxed (298 K) and the non-relaxed enzyme forms (77 K) indicate conformational changes proceeding in the relaxed form after reduction of the heme iron which lead to altered interactions between the active centre and its environment in the protein. The two maxima of the nonequilibrium form of cytochrome P-450 without substrate in the visible absorption spectrum (alpha-band, beta-band) and the ratio of their intensities indicate the low-spin character of the heme iron. These spectral properties give evidence for a reduced cytochrome P-450 with two heme-linked axial ligands.

Animals↗
PubMed1975

Studies on the conformational changes of metalloproteins induced by electrons in water-ethylene glycol solutions at low temperatures. III. Adrenal ferredoxin.

The reduction of adrenal ferredoxin (adrenodoxin) at low temperatures was investigated in order to separate local modifications of the active centre of the protein on its reduction, from the conformational transition which seems to accompany the change of the redox state of the irons; The ESR spectra of the states of the protein, where the reduced active centre is to be found by the "oxidized" conformation of the apoprotein, were obtained. The transition from the states of the protein to the state which occurs on its chemical reduction at room temperature was also investigated. The results of the work support the view that conformational changes in proteins (enzymes) which take place while they are functioning proceed after modifications of the active centres (change of the redox state, adsorption of a substrate, etc.), and are essentially caused by them. Adrenal ferredoxin was the third subject in our studies of the intermediate states of proteins which appear after reduction of their active centres by means of electrons trapped in water-ethylene glycol mixtures at the temperature of liquid nitrogen [1, 2]. In the reduced state, the active centre of the protein has an ESR signal with a g-factor of 1.94 [3, 4] which is convenient for our purposes.

Adrenodoxin↗