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1.
14N-ENDOR evidence for imidazole coordination in copper proteins 总被引:1,自引:0,他引:1
H Yokoi 《Biochemical and biophysical research communications》1982,108(3):1278-1284
14N-ENDOR studies of simple nitrogen-coordinated copper(II) complexes in frozen aqueous solutions show that the nitrogen hyperfine constants, A″ and A⊥, of imidazole are much more isotropic () than those of the other biologically-related ligand nitrogens. From this result, combined with 14N-ENDOR results of some copper proteins containing imidazoles as ligands, it is concluded that R < 1.10 for nitrogen hyperfine constants can be employed as an empirical criterion for demonstration of the existence of imidazole coordination in copper proteins. 相似文献
2.
A. J. Hoff 《European biophysics journal : EBJ》1982,8(3):107-150
The primary reactants in photosynthesis are defined as the chemical entities on which charges are generated and stabilized after capture of a photon by the photochemical trap: PIX
hv
P
*
IX P
+
I
–
X P
+
IX
–, where P stands for the primary electron donor, P
* for its excited singlet state, I for the first (ESR-detectable) electron acceptor and X for the secondary acceptor complex. The ESR and ENDOR experiments which have played a rÔle in the identification and characterization of P, I, and X in the bacterial and plant photosystems are comprehensively reviewed. The structural and kinetic information obtained with magnetic resonance techniques are integrated with results obtained with optical spectroscopy to give a unified picture of the pathway of primary photochemistry in photosynthesis.
Nomenclature of Primary Reactants
In the interest of uniformity this review introduces a nomenclature of the primary reactants that deviates in some respects from the commonly used labels. The nametags used here and listed below are abbreviations of the molecules that are identified as primary reactants, with the exception of the donors, for which I have retained the commonly accepted designation. Photosystems: PS 1, photosystem 1 of plants; PS 2, photosystem 2 of plants; pBPS, the photosystem of purple bacteria; gBPS, ditto of green bacteria. P: Primary donors: P700 (PS 1), P680 (PS 2), P860 (generic label for BChl a containing purple bacteria), P960 (generic label for BChl b containing purple bacteria), P840 (generic name for green bacteria). I: First acceptors: Chl a (PS 1), Ph a (PS 2), BPh a,b (pBPS). X: Secondary acceptors: F
x
(PS 1), pQ
1 (PS 2), uQ
1 or mQ
1 (pBPS), B (gBPS). Tertiary acceptors: F
A,B
(PS 1), pQ
2 (PS 2), uQ
2 (pBPS), F
1 (gBPS).This paper is based on a lecture given at the Joint Meeting of the Belgium, German (FRG), and Netherlands Societies for Biophysics, Aachen 1980 相似文献
3.
Picosecond and nanosecond spectroscopic techniques have been used to study the primary electron transfer processes in reaction centers isolated from the photosynthetic bacterium Rhodopseudomonas viridis. Following flash excitation, the first excited singlet state (P1) of the bacteriochlorophyll complex (P) transfers an electron to an intermediate acceptor (I) in less than 20 ps. The radical pair state (P+I?) subsequently transfers an electron to another acceptor (X) in about 230 ps. There is an additional step of unknown significance exhibiting 35 ps kinetics. P+ subsequently extracts an electron from a cytochrome, with a time constant of about 270 ns. At low redox potential (X reduced before the flash), the state P+I? (or PF) lives approx. 15 ns. It decays, in part, into a longer lived state (PR), which appears to be a triplet state. State PR decays with an exponential time of approx. 55 μs. After continuous illumination at low redox potential (I and X both reduced), excitation with an 8-ps flash produces absorption changes reflecting the formation of the first excited singlet state, P1. Most of P1 then decays with a time constant of 20 ps. The spectra of the absorbance changes associated with the conversion of P to P1 or P+ support the view that P involves two or more interacting bacteriochlorophylls. The absorbance changes associated with the reduction of I to I? suggest that I is a bacteriopheophytin interacting strongly with one or more bacteriochlorophylls in the reaction center. 相似文献
4.
《Free radical research》2013,47(1-2):63-68
α-2.6-Difluorophenyl-N-tert-butylnitrone (F2PBN) was synthesized and evaluated. A number of alkyl adducts of F2PBN were studied by ESR/ENDOR. An additional hyperfine splitting (a triplet of doublets of doublets) is reported. The existence of two (one large, one small) F-hfsc's from the ortho-fluorine atoms in the phenyl ring of most alkyl adducts was confirmed by ENDOR spectroscopy. 相似文献
5.
6.
Pyruvate formate lyase activating enzyme is a member of a novel superfamily of enzymes that utilize S-adenosylmethionine to initiate radical catalysis. This enzyme has been isolated with several different iron-sulfur clusters, but single turnover monitored by EPR has identified the [4Fe-4S](1+) cluster as the catalytically active cluster; this cluster is believed to be oxidized to the [4Fe-4S](2+) state during turnover. The [4Fe-4S] cluster is coordinated by a three-cysteine motif common to the radical/S-adenosylmethionine superfamily, suggesting the presence of a unique iron in the cluster. The unique iron site has been confirmed by Mossbauer and ENDOR spectroscopy experiments, which also provided the first evidence for direct coordination of S-adenosylmethionine to an iron-sulfur cluster, in this case the unique iron of the [4Fe-4S] cluster. Coordination to the unique iron anchors the S-adenosylmethionine in the active site, and allows for a close association between the sulfonium of S-adenosylmethionine and the cluster as observed by ENDOR spectroscopy. The evidence to date leads to a mechanistic proposal involving inner-sphere electron transfer from the cluster to the sulfonium of S-adenosylmethionine, followed by or concomitant with C-S bond homolysis to produce a 5'-deoxyadenosyl radical; this transient radical abstracts a hydrogen atom from G734 to activate pyruvate formate lyase. 相似文献
7.
Alexander M. Khenkin Debbie Baute Andrei V. Astashkin Daniella Goldfarb Ronny Neumann 《Inorganica chimica acta》2006,359(9):3072-3078
An EPR spectrum of as synthesized [G.A. Tsigdinos, C.J. Hallada, Inorg. Chem. 7 (1968) 437-441], orange colored, H5PV2Mo10O40 polyoxometalate showed the presence of a reduced vanadium(IV) addenda atom. Surprisingly, further 31P ENDOR (electron-nuclear double resonance) measurements indicated the absence of a phosphorous heteroatom leading to the suggestion that H5VVVIVMo11O40 exists as a previously unrecognized impurity in the typically synthesized H5PV2Mo10O40 compound. H5/4PVVO4VIV/VMo11O36 was then synthesized in low yield (0.8 mol%) by omitting the addition of phosphate in a typical H5PV2Mo10O40 preparation. The molecular formulation and structure was supported by X-ray crystallography, infrared and mass spectrometry. Further use of EPR/ENDOR/ESEEM (electron-spin echo envelope modulation) allowed the formulation of [VVVIVMo11O40]5− as [VVO4VIVMo11O36]5−. Accordingly, the polyoxometalate has a heteroatom core with 11 molybdenum addenda and one VO2+ moiety at the polyoxometalate surface. The redox potential and the catalytic activity of the new vanadomolybdate polyoxometalate compound were essentially identical to the often-studied H5PV2Mo10O40 polyoxometalate isomeric mixture. 相似文献
8.
Marilena Di Valentin Stefano Ceola Giorgio Mario Giacometti Orlando Crescenzi Donatella Carbonera 《BBA》2008,1777(3):295-307
The photoexcited triplet state of the carotenoid peridinin in the Peridinin-chlorophyll a-protein of the dinoflagellate Amphidinium carterae has been investigated by pulse EPR and pulse ENDOR spectroscopies at variable temperatures. This is the first time that the ENDOR spectra of a carotenoid triplet in a naturally occurring light-harvesting complex, populated by energy transfer from the chlorophyll a triplet state, have been reported. From the electron spin echo experiments we have obtained the information on the electron spin polarization dynamics and from Mims ENDOR experiments we have derived the triplet state hyperfine couplings of the α- and β-protons of the peridinin conjugated chain. Assignments of β-protons belonging to two different methyl groups, with aiso = 7.0 MHz and aiso = 10.6 MHz respectively, have been made by comparison with the values predicted from density functional theory. Calculations provide a complete picture of the triplet spin density on the peridinin molecule, showing that the triplet spins are delocalized over the whole π-conjugated system with an alternate pattern, which is lost in the central region of the polyene chain. The ENDOR investigation strongly supports the hypothesis of localization of the triplet state on one peridinin in each subcluster of the PCP complex, as proposed in [Di Valentin et al. Biochim. Biophys. Acta 1777 (2008) 186-195]. High spin density has been found specifically at the carbon atom at position 12 (see Fig. 1B), which for the peridinin involved in the photo-protective mechanism is in close contact with the water ligand to the chlorophyll a pigment. We suggest that this ligated water molecule, placed at the interface between the chlorophyll-peridinin pair, is functioning as a bridge in the triplet-triplet energy transfer between the two pigments. 相似文献
9.
Miwa Sugiura Tania Tibiletti Itsuki Takachi Yuya Hara Shin Kanawaku Julien Sellés Alain Boussac 《BBA》2018,1859(12):1259-1273
In Photosystem II (PSII), the Mn4CaO5-cluster of the active site advances through five sequential oxidation states (S0 to S4) before water is oxidized and O2 is generated. The V185 of the D1 protein has been shown to be an important amino acid in PSII function (Dilbeck et al. Biochemistry 52 (2013) 6824–6833). Here, we have studied its role by making a V185T site-directed mutant in the thermophilic cyanobacterium Thermosynechococcus elongatus. The properties of the V185T-PSII have been compared to those of the WT*3-PSII by using EPR spectroscopy, polarography, thermoluminescence and time-resolved UV–visible absorption spectroscopy. It is shown that the V185 and the chloride binding site very likely interact via the H-bond network linking TyrZ and the halide. The V185 contributes to the stabilization of S2 into the low spin (LS), S?=?1/2, configuration. Indeed, in the V185T mutant a high proportion of S2 exhibits a high spin (HS), S?=?5/2, configuration. By using bromocresol purple as a dye, a proton release was detected in the S1TyrZ?→?S2HSTyrZ transition in the V185T mutant in contrast to the WT*3-PSII in which there is no proton release in this transition. Instead, in WT*3-PSII, a proton release kinetically much faster than the S2LSTyrZ?→?S3TyrZ transition was observed and we propose that it occurs in the S2LSTyrZ?→?S2HSTyrZ intermediate step before the S2HSTyrZ?→?S3TyrZ transition occurs. The dramatic slowdown of the S3TyrZ?→?S0TyrZ transition in the V185T mutant does not originate from a structural modification of the Mn4CaO5 cluster since the spin S?=?3?S3 EPR signal is not modified in the mutant. More probably, it is indicative of the strong implication of V185 in the tuning of an efficient relaxation processes of the H-bond network and/or of the protein. 相似文献
10.
Zein S Kulik LV Yano J Kern J Pushkar Y Zouni A Yachandra VK Lubitz W Neese F Messinger J 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1494):1167-77; discussion 1177
Nature invented a catalyst about 3Gyr ago, which splits water with high efficiency into molecular oxygen and hydrogen equivalents (protons and electrons). This reaction is energetically driven by sunlight and the active centre contains relatively cheap and abundant metals: manganese and calcium. This biological system therefore forms the paradigm for all man-made attempts for direct solar fuel production, and several studies are underway to determine the electronic and geometric structures of this catalyst. In this report we briefly summarize the problems and the current status of these efforts and propose a density functional theory-based strategy for obtaining a reliable high-resolution structure of this unique catalyst that includes both the inorganic core and the first ligand sphere. 相似文献