Identification of the six ligands to manganese(II) in transition-state-analogue complexes of creatine kinase: oxygen-17 superhyperfine coupling from selectively labeled ligands

The complete coordination scheme for Mn(II) in transition-state-analogue complexes with creatine kinase has been determined by electron paramagnetic resonance (EPR) spectroscopy. Perturbations in the EPR spectra for Mn(II) due to superhyperfine coupling to 17O of selectively labeled ligands have been used to identify oxygen ligands in the first coordination sphere of the metal ion. The results show that in the complex of enzyme-MnADP-formate-creatine, Mn(II) is bound to oxygen ligands from both the alpha- and beta-phosphate groups of ADP, to an oxygen from the carboxylate group of formate, and to three water molecules. In the complex with thiocyanate replacing formate as the stabilizing anion, previous infrared experiments [Reed, G. H., Barlow, C. H., & Burns, R. A., Jr. (1978) J. Biol. Chem. 253, 4153-4158] indicated that the nitrogen from thiocyanate was bound to the Mn(II). The magnitudes of the 17O superphyperfine coupling constants from the O- ligands of the ADP phosphate groups and from the formate carboxylate are approximately equal and are larger than that for the water ligands. The symmetry of the zero-field-splitting tensor for Mn(II) indicates that the oxygens from the alpha- and beta-phosphate groups of ADP and the ligand donor atom from the anion occupy mutually cis positions in the octahedral coordination geometry. Water proton relaxation time measurements show that the three water molecules which are bound to Mn(II) are not in free exchange with the bulk solvent. Hence, an enclosed structure at the active site is indicated. The results suggest that for creatine kinase the activating metal ion is bound to all three phosphate groups in the transition state of the reaction.     

The stoichiometry and stability of the NADP complexes with manganese(II) ions as studied by electron paramagnetic resonance.

Magnetic resonance techniques have been applied to study the stability of the complexes formed between Mn(II) ions and NADP in aqueous solutions at a pH of 7.5 and 20 degrees C. The electron paramagnetic resonance (epr) data indicate that at low Mn(II) ion concentrations ([Mn(II)] less than 1 mM; [NADP] approximately 5 mM), a 1:1 complex is formed with an apparent stability constant K1 = 370 +/- 50 M-1 at an ionic strength of 0.22 in the presence of 0.20 M Cl-. At high Mn(II) ion concentrations, a Mn(II)2-NADP species, with an apparent stability constant K2 = 54 +/- 17 M-1, is present in significant amounts. When the epr data are corrected for the presence of the MnCl+ ion, the analysis of the new Scatchard plot yields stability constants for the two sites of K1 = 640 +/- 90 M-1 and K2 = 88 +/- 13 M-1, respectively. The presence of two metal ion binding sites on the NADP molecule has not been observed previously, and previous workers have always analyzed their data in terms of the 1:1 Mn(II)-NADP complex. An epr temperature study of K1 yields a value of delta H equal to 1.3 +/- 0.2 kcal/mol (1 cal = 4.187 J).     

Binding of manganese(II) to a tertiary stabilized hammerhead ribozyme as studied by electron paramagnetic resonance spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is used to study the binding of MnII ions to a tertiary stabilized hammer-head ribozyme (tsHHRz) and to compare it with the binding to the minimal hammerhead ribozyme (mHHRz). Continuous wave EPR measurements show that the tsHHRz possesses a single high-affinity MnII binding site with a KD of < or =10 nM at an NaCl concentration of 0.1 M. This dissociation constant is at least two orders of magnitude smaller than the KD determined previously for the single high-affinity MnII site in the mHHRz. In addition, whereas the high-affinity MnII is displaced from the mHHRz upon binding of the aminoglycoside antibiotic neomycin B, it is not from the tsHHRz. Despite these pronounced differences in binding, a comparison between the electron spin echo envelope modulation and hyperfine sublevel correlation spectra of the minimal and tertiary stabilized HHRz demonstrates that the structure of both binding sites is very similar. This suggests that the MnII is located in both ribozymes between the bases A9 and G10.1 of the sheared G . A tandem base pair, as shown previously and in detail for the mHHRz. Thus, the much stronger MnII binding in the tsHHRz is attributed to the interaction between the two external loops, which locks in the RNA fold, trapping the MnII in the tightly bound conformation, whereas the absence of long-range loop-loop interactions in the mHHRz leads to more dynamical and open conformations, decreasing MnII binding.     

Synthesis and spectral investigation of manganese(II), cadmium(II) and oxovanadium(IV) complexes with 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone): Crystal structure of manganese(II) and cadmium(II) complexes

The chelating behavior of 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) (H₂dapa) towards manganese(II), cadmium(II) and oxovanadium(IV) ions has been studied by elemental analyses, conductance measurements, magnetic properties and spectral (IR, ¹H NMR, UV-Vis and EPR) studies. The IR spectral studies suggest the pentadentate nature of the ligand with pyridine nitrogen, two azomethine nitrogens and two carbonyl oxygen atoms as the ligating sites. Six coordinate structure for [VO(H₂dapa)]SO₄ · H₂O and seven coordinate structures for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)Cl₂] · H₂O complexes have been proposed. Pentagonal bipyramidal geometry for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)(Cl₂)] · H₂O complexes was confirmed by single crystal analysis. The X-band EPR spectra of the oxovanadium(IV) and manganese(II) complexes in the polycrystalline state at room (300 K) and also at liquid nitrogen temperature (77 K) were recorded and their salient features are reported.     

Interaction of manganese (II) with valinomycin: observation of mixed complexes

The interaction of antibiotic valinomycin with manganese (II) has been studied using circular dichroism, electron spin resonance and infrared techniques. Results show that Mn(II) forms complexes with valinomycin in both 2:1 (valinomycin-ion-valinomycin sandwich) and 1:1 (equimolar) stoichiometries. The 1:1 type observed here is very different from the well known K⁺-valinomycin bracelet conformation.     

Multifrequency electron spin-echo envelope modulation studies of nitrogen ligation to the manganese cluster of photosystem II

The CalEPR Center at UC-Davis (http://brittepr.ucdavis.edu) is equipped with five research grade electron paramagnetic resonance (EPR) instruments operating at various excitation frequencies between 8 and 130GHz. Of particular note for this RSC meeting are two pulsed EPR spectrometers working at the intermediate microwave frequencies of 31 and 35GHz. Previous lower frequency electron spin-echo envelope modulation (ESEEM) studies indicated that histidine nitrogen is electronically coupled to the Mn cluster in the S2 state of photosystem II (PSII). However, the amplitude and resolution of the spectra were relatively poor at these low frequencies, precluding any in-depth analysis of the electronic structure properties of this closely associated nitrogen nucleus. With the intermediate frequency instruments, we are much closer to the 'exact cancellation' limit, which optimizes ESEEM spectra for hyperfine-coupled nuclei such as 14N and 15N. Herein, we report the results from ESEEM studies of both 14N- and 15N-labelled PSII at these two frequencies. Spectral simulations were constrained by both isotope datasets at both frequencies, with a focus on high-resolution spectral examination of the histidine ligation to the Mn cluster in the S2 state.     

Hydrogen-bonded supramolecular manganese(II) complexes with network and sheet structures bridged by terephthalate unit

Two 1D complexes [Mn(4- methylpyrazole)₃(H₂O)(tp)]_n (2) and [Mn(4-methylpyrazole)₄(tp)]_n (3) (tp = terephthalate) were synthesized and characterized by means of X-ray analysis and magnetic studies. The molecular structure of 2 reveals that Mn(II) centers with asymmetric coordination surroundings are bridged by crystallographically different tp ligands, forming a 1D chain. The 1D coordination chains are interconnected by hydrogen bonds between free carboxylate oxygen atoms in a chain and hydrogens of pyrazole nitrogen atoms in neighboring chains, leading to a 3D framework. Compound 3 also exhibits a 1D coordination chain which is hydrogen-bonded to adjacent chains, providing a 2D sheet structure. Interestingly, the structures include intra- and interchain hydrogen bonds contributed from N-H groups of the capping 4-methylpyrazole ligands. Magnetic measurements show weak antiferromagnetic interactions with exchange coupling parameters of J = −0.018 cm⁻¹ for 2 and J = −0.062 cm⁻¹ for 3 through the extended tp ligand on the basis of an infinite chain model (H = −J∑S_i · S_i + 1).     

Interaction of manganese II ions with proteins

Electron and ESR-spectroscopic study was carried out of the interaction between manganese(II) ions with albumine and lysozome in water solutions at different manganese concentrations and ratios manganese/protein. The results obtained suggest presence of metal-protein interactions. At high manganese concentrations liotropic effect is observed. At high molecular ratios protein/manganese and manganese concentrations close to physiological ones formation of coordination compounds manganes(II) ions with proteins was observed.     

Determination of the interaction of ADP and dADP with copper(II), manganese(II) and lanthanide(III) ions by nuclear-magnetic-resonance spectroscopy.

The aqueous solution conformation of the 1:1 complexes of ADP and dADP bound to a lanthanide ion have been determined by examination of the dipolar shifts and induced relaxation at pH 6.4. Apparent inconsistencies in the observed data are interpreted in terms of a gradually changing lanthanide-oxygen bond length from Pr3+ to Yb3+. The conformations of ADP and dADP are very similar showing an extended diphosphate, a 2E ribose conformation and with the adenine base displaying a small syn contribution. Relaxation data obtained from Mn(II) titrations are readily interpreted in terms of bidentate coordination to alpha and beta phosphates with the nucleotides retaining the same overall conformation found from the lanthanide study. No evidence to support an intramolecular water-bridged backbound structure is observed. The interaction with Cu(II) is more complex, coordination is observed not only at the diphosphate but also at two sites on the base, N-1, and the chelate formed between N-7 and the amino group. The relative importance of these sites is different for ADP and dADP and is also pH-dependent for ADP.     

Characterization of dioxygenated cobalt(II)-carnosine complexes by Raman and IR spectroscopy

Raman and IR studies are carried out on carnosine (beta-alanyl-L-histidine, Carnos) and its complexes with cobalt(II) at different metal/ligand ratios and basic pH. Binuclear complexes that bind molecular oxygen are formed and information regarding the O-O bridge is obtained from the Raman spectra. When the Co(II)/Carnos ratio is 相似文献   

Site-specific electronic couplings in dyads with MLCT excited states. Intramolecular energy transfer in isomeric Ru(II)-Ru(II) cyclometalated complexes.

The rod-like binuclear complexes [(ttpy)Ru(tpy-ph(2)-phbpy)Ru(ttpy)](4+) and [(ttpy)Ru(tpy-ph(2)-tpy)Ru(phtbpy)](4+) (for abbreviations, see text) have been synthesized and characterized. In both complexes, the polypyridine Ru(II) centers have (N--N--N)Ru(N--N--N) and (N--N--N)Ru(C--N--N) coordination environment. The two isomeric species differ in whether the cyclometalating carbon resides on the bridging or on the terminal ligand. The two complexes have virtually identical energy levels, but MLCT excited states of different (bridging or terminal) ligand localization. They are thus ideally suited to investigate possible effects of excited-state localization on intramolecular energy transfer kinetics. In fact, ultrafast spectroscopic measurements yield different energy transfer time constants for the two isomers, with the bridge-cyclometalated complex (2.7 ps) being faster than the terminal-cyclometalated one (8.0 ps). This difference can be explained in terms of different electronic factors for Dexter energy transfer. The study highlights the peculiar intricacies of intramolecular energy transfer in inorganic dyads involving MLCT excited states.     

Manganese(II) complexes with V-shaped sulfonyldibenzoate: The 3D structures with interpenetrated threefold or tetra-nuclear manganese(II) units

Five Mn^II-sdba coordination polymers with mono-, di-, tri-, tetra-nuclear cores based on the V-shaped 4,4′-dicarboxybiphenyl sulfone (H₂sdba) ligands: [Mn(sdba)(phen)₂(H₂O)]_n·3nH₂O (1), [Mn₂(sdba)₂(μ-H₂O)(py)₄]_n (2), [Mn₃(sdba)₂(Hsdba)₂(2,2′-bipy)₂]_n (3), [Mn₄(sdba)₄(4-mepy)₂(H₂O)₄]_n·2nH₂O (4) and [Mn₄(sdba)₄(bpp)₄(μ-H₂O)₂]_n·0.5nH₂O (5) (phen = 1,10-phenanthroline, 2,2′-bipy = 2,2′-bipyridine, 4-mepy = 4-picoline, bpp = 1,3-bi(pyridine-4-yl)propane) were hydrothermally synthesized and structurally characterized. The M-O-C metal clusters in above complexes act as SBUs, and the V-shaped sdba ligands link the SBUs to generate the novel frameworks. In complexes 1 and 3 their 1D chains are linked into the 2D planes through various hydrogen bonding. Complex 2 displays the 3D structure with interpenetrated threefold, while complexes 4 and 5 both exhibit the 3D structures with the tetra-nuclear Mn₄ units. The magnetic susceptibility studies in the 2-300 K range for these complexes reveal the existence of anti-ferromagnetic exchange interactions between the Mn^II ions.     

Nuclear magnetic resonance spectroscopy of cobalt (II) porphyrin-quinone complexes

Weak intermolecular complexes of cobalt(II) and nickel(II) mesoporphyrin dimethyl ester with 1,4-naphthoquinone, vitamin K-3, vitamin K-1 and ubiquinone 30 have been detected by ¹H-NMR spectroscopy in chloroform solutions. The relative orientation of the components of complexes is discussed.     

Synthesis, crystal structures and spectroscopy of meclofenamic acid and its metal complexes with manganese(II), copper(II), zinc(II) and cadmium(II). Antiproliferative and superoxide dismutase activity

Some new complexes of meclofenamic acid (N-(2,6-dichloro-m-tolyl)anthranilic acid), Hmeclo (1), with potentially interesting biological activities are described. Complexes [Mn(meclo)₂] (2), [Cu(meclo)₂(H₂O)₂] (3), [Zn(meclo)₂(H₂O)₂] (4) and [Cd(meclo)₂(H₂O)₂] (5) were prepared and structurally characterized by means of vibrational, electronic and ¹H and ¹³C NMR spectroscopies. The crystal structure of complexes [Cu₄(meclo)₆(OH)₂(DMSO)₂]2DMSO (3a) and [Cd(meclo)₂(DMSO)₃] (5a) have been determined by X-ray crystallography. Complex (3a) is a centrosymmetric tetramer built up around the planar cyclic Cu₂(OH)₂ unit. Complex 5a is mononuclear seven-coordinated complex with the meclofenamato ligand behaving as a bidentate deprotonated chelating ligand. Intra and intermolecular hydrogen bonds stabilize these two structures, while the crystal packing is determined by π-π and C−H−-π interactions. Meclofenamic acid and its metal complexes have been evaluated for antiproliferative activity in vitro against the cells of three human cancer cell lines, MCF-7 (breast cancer cell line), T24 (bladder cancer cell line), and A-549 (non-small cell lung carcinoma), and a mouse fibroblast L-929 cell line. Complex 5 exhibits the highest selectivity against MCF-7 and 4 shows the highest selectivity against T-24. Complexes 2-5 were found to be more potent cytotoxic agents against T-24 and complex 5 against MCF-7 cancer cell lines than the prevalent benchmark metallodrug, cis-platin. The superoxide dismutase activity was measured by the Fridovich test which showed that complex [Cu(meclo)₂(H₂O)₂] is a good superoxide scavenger.     

Structures of manganese(II) complexes with ATP, ADP, and phosphocreatine in the reactive central complexes with creatine kinase: electron paramagnetic resonance studies with oxygen-17-labeled ligands

Coordination of Mn(II) to the phosphate groups of the substrates and products in the central complexes of the creatine kinase reaction mixture has been investigated by electron paramagnetic resonance (EPR) spectroscopy with regiospecifically 17O-labeled substrates. The EPR pattern for the equilibrium mixture is a superposition of spectra for the two central complexes, and this pattern differs from those observed for the ternary enzyme-Mn(II)-nucleotide complexes and from that for the dead-end complex enzyme-Mn(II)ADP-creatine. In order to identify those signals that are associated with each of the central complexes of the equilibrium mixture, spectra were obtained for a complex of enzyme, Mn(II)ATP, and a nonreactive analogue of creatine, 1-(carboxymethyl)-2-iminoimidazolidin-4-one, which is a newly synthesized competitive inhibitor. This inhibitor permits an unobstructed view of the EPR spectrum for Mn(II)ATP in the closed conformation of the active site. The EPR spectrum for this nonreactive complex with Mn(II)ATP matches one subset of signals in the spectrum for the equilibrium mixture, i.e., those due to the enzyme-Mn(II)-ATP-creatine complex. Chemical quenching of the samples followed by chromatographic assays for both ATP and ADP indicates that the enzyme-Mn(II)ADP-phosphocreatine and the enzyme-Mn(II)ATP-creatine complexes are present in a ratio of approximately 0.7 to 1. A similar value for the equilibrium constant for enzyme-bound substrates is obtained directly from the EPR spectrum for the equilibrium mixture.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potentiometric study of vitamin D3 complexes with manganese(II), iron(II), iron(III) and zinc(II) in water-ethanol medium.

Vitamin D3 (LH) complexes with manganese(II), iron(II), iron(III) and zinc(II) were identified in water-ethanol medium (30/70). Their stability constants were determined at 298 K and at a constant ionic strength of 0.100 M using potentiometric methods. The computerisation of the experimental data showed the presence of ML (M = metal, L = deprotonated vitamin D3) and ML2 species in all cases; in addition, the ML3 iron(III) complex was detected. The calculated overall stability constants beta for MnIIL, FeIIL, FeIIIL and ZnIIL are, respectively, in logarithms, 12.4, 16.5, 28.5 and 16.5. Under the experimental conditions, the only protonated species MLH detected was with iron(III).     

Electron-paramagnetic-resonance studies of manganese(II) complexes with elongation factor Tu from Bacillus stearothermophilus. Observation of a GTP hydrolysis intermediate state complex

Changes in the coordination of Mn2+ to nucleotide, water and protein at the active site of elongation factor Tu (EF-Tu) have been studied by electron paramagnetic resonance (EPR) spectroscopy. From the time dependence of the Mn2+ spectrum after addition of GTP to EF-Tu X Mn, it was apparent that three complexes with different EPR linewidths could be detected. Using additional information from the kinetics of 32Pi production and release from EF-Tu X Mn X [gamma-32P]GTP these were identified as EF-Tu X Mn X GTP (linewidth 4.2 mT), EF-Tu X Mn X GDP X Pi (1.20 mT) and EF-Tu X Mn X GDP (1.29 mT). The linewidth for EF-Tu X Mn was 1.51 mT. The rate constant for GTP cleavage on EF-Tu was 0.01 min-1 at 24 C, for Pi release from the EF-Tu X GDP X Pi complex 0.0033 min-1. The corresponding rate constants in the presence of Mg2+ were 0.003 min-1 and 0.0065 min-1. The rate constant for reversal of the cleavage step was found to be much smaller than that for the rate of Pi release (and consequently much smaller than in the forward direction), as shown by 31P-NMR experiments on the incorporation of 18O into Pi from GTP hydrolyzed in the presence of H2 18O. EPR experiments using specifically 17O-labelled GTPs demonstrated an interaction of Mn2+ with the beta-phosphate in both the EF-Tu X GDP X Pi and EF-Tu X GDP complexes. Inorganic phosphate in the EF-Tu X GDP X Pi complex was found not to interact with the metal ion. From EPR experiments in H2 17O, it was concluded that the most probable number of water molecules in the different complexes was 4 (EF-Tu X Mn), 5 (EF-Tu X Mn X GDP X Pi) and 3 (EF-Tu X Mn X GDP), with 2, 0 and 2 metal-protein interactions respectively.