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1.
The effects of ligands with various field strengths on the optical absorption spectrum of myeloperoxidase have been investigated. As is the case with other hemoproteins, the Soret peak in the optical absorption spectra at 77 K moves to longer wavelengths when strong-field ligands are present, whereas binding of such ligands as chloride and fluoride, which stabilize the high-spin state, shows the opposite effect. With a ligand of intermediate field strength, such as azide, the optical spectrum is not affected at room temperature, but lowering of the temperature results in the formation of the low-spin form of the enzyme. Similarly, in native myeloperoxidase a spin state equilibrium is found in which the low-spin state is favoured at high ionic strength and displays corresponding changes in the optical spectra. From the ligand- and the temperature-induced changes in the optical spectra of the ferric enzyme it is concluded that the band at 620-630 nm is an alpha band of the low-spin heme iron species, whereas the bands at 500 and 690 nm are probably 'charge-transfer' bands of the heme with the iron in the high-spin state.  相似文献   

2.
Mononuclear zinc complexes of a family of pyridylmethylamide ligands abbreviated as HL, HLPh, HLMe3, HLPh3, and MeLSMe [HL = N-(2-pyridylmethyl)acetamide; HLPh = 2-phenyl-N-(2-pyridylmethyl)acetamide; HLMe3 = 2,2-dimethyl-N-(2-pyridylmethyl)propionamide; HLPh3 = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide; MeLSMe = N-methyl-2-methylsulfanyl-N-pyridin-2-ylmethyl-acetamide] were synthesized and characterized spectroscopically and by single crystal X-ray structural analysis. The reaction of zinc(II) salts with the HL ligands yielded complexes [Zn(HL)2(OTf)2] (1), [Zn(HL)2(H2O)](ClO4)2 (2), [Zn(HLPh3)2(H2O)](ClO4)2 (3), [Zn(HLPh)Cl2] (4), [Zn(HLMe3)Cl2] (5), and [Zn(MeLSMe)Cl2] (6). The complexes are either four-, five- or six-coordinate, encompassing a variety of geometries including tetrahedral, square-pyramidal, trigonal-bipyramidal, and octahedral.  相似文献   

3.
Cytochromes c' have been isolated from six strains of Achromobacter xylosoxidans: NCIB 11015 (formerly Alcaligenes sp. NCIB 11015), GIFU 543, 1048, 1051, 1055 and 1764. They are dimeric proteins with more positive redox potentials than those of cytochromes c' from phototrophic bacteria at neutral pH. The electronic absorption, EPR and MCD spectra on NO-ferrous cytochromes c' at physiological pH showed that the major part of the heme-iron of nitrosylheme was penta-coordinated. The EPR spectral results indicated that the ground state of the heme-iron of ferric cytochromes c' appears to be in an admixed spin states which consists of predominant high-spin with a slight intermediate-spin character at pH 7.2. These spectra were compared with those for cytochromes c' from phototrophic bacteria and the other hemoproteins.  相似文献   

4.
Human recombinant myeloperoxidase (recMPO), purified from an engineered Chinese hamster ovary (CHO) cell line, has been characterized and compared to the mature enzyme isolated from polymorphonuclear leukocytes. Both molecules appear essentially similar in physicochemical enzymatic terms according to the following observations. 1. The unprocessed recombinant protein displays the characteristic light absorption spectra of ferric mature MPO and exhibits its typical spectral changes in the presence of dithionite or hydrogen peroxide. 2. The addition of 14C-labeled 5-aminolevulinic acid, a heme precursor, to the culture medium of recombinant CHO cells yields labeled recMPO, indicating the presence of a heme-like structure in the molecule. 3. Like mature MPO, recMPO has a peroxidatic activity and catalyzes the oxidation of chloride ions in the presence of hydrogen peroxide, producing hypochlorous acid as measured by the monochlorodimedon assay. For both enzymes, the chlorinating activity optimally occurs around pH 5.0 at about 100 microM of hydrogen peroxide and is strongly inhibited by methimazole. 4. Diethylpyrocarbonate significantly reduces the enzymatic activity of both molecules, suggesting that histidine residues may be of prime importance in the active site of the enzymes. 5. According to infrared spectroscopy data, both enzymes present a very similar secondary structure organization. In conclusion, the data suggest that the processing of the precursor enzyme (recMPO) into the mature form occurs without major structural and functional consequences.  相似文献   

5.
6.
Superoxide and myeloperoxidase (MPO) are essential for the oxidative killing of bacteria by neutrophils. Previously, we developed a kinetic model to demonstrate that within the confines of neutrophil phagosomes, superoxide should react exclusively with MPO and be converted to hypochlorous acid. The model consists of all known reactions and rate constants for reactions of superoxide, hydrogen peroxide, and chloride ions with MPO, except for the reaction of superoxide with compound I, which could only be estimated. Compound I is a transitory redox intermediate of MPO that is responsible for oxidizing chloride ions to hypochlorous acid. To tackle the challenge of observing the reaction between two transient species, we combined stopped-flow spectrophotometry with pulse radiolysis. Using this technique, we directly observed the reduction of compound I by superoxide. The rate constant for the reaction was determined to be 5.6±0.3×10(6)M(-1)s(-1). This value establishes superoxide as one of the best substrates for compound I. Based on this value, the rate constant for reduction of compound II by superoxide was determined to be 1.2±0.1×10(6)M(-1)s(-1). Within phagosomes, the reduction of compound I by superoxide will compete with the oxidation of chloride ions so that the relative concentrations of these two substrates will affect the yield of hypochlorous acid. Characterization of this reaction confirms that superoxide is a physiological substrate for MPO and that their interactions are central to an important host defense mechanism.  相似文献   

7.
The first evidence of multi-component complexes formed by myeloperoxidase (MPO), ceruloplasmin (CP), and very low/low density lipoproteins (VLDL/LDL) obtained by electrophoresis, gel filtration, and photon-correlation spectroscopy (PCS) is presented in this paper. Complexes were observed when isolated MPO, CP, and VLDL/LDL were mixed and/or when MPO was added to the blood plasma. Complex LDL–MPO–CP was detected in 44 of 100 plasma samples taken from patients with atherosclerosis, and 33 of 44 samples also contained the VLDL–MPO–CP complex. MPO concentration in these patients’ plasma exceeded 800 ng/ml. Interaction of MPO with high density lipoproteins (HDL) was not revealed, as well as binding of CP to lipoproteins in the absence of MPO. Adding antibodies against apoB-100 to VLDL–MPO–CP and LDL–MPO–CP complexes results in release of lipoproteins. Using PCS the diameters of complexes under study were evaluated. By comparing concentrations of the components in complexes formed by MPO, CP, and lipoproteins their stoichiometry was assessed as 2VLDL:1MPO:2CP and 1LDL:1MPO:2CP. Lipoproteins affected the inhibition of MPO peroxidase activity by CP. The affinity of lipoproteins to MPO–CP complex was assessed using apparent dissociation constants determined as ~0.3 nM for VLDL and ~0.14 nM for LDL.  相似文献   

8.
The spectral and functional properties of carotenoids associated with each of the two light-harvesting complexes of the Rhodopseudomonas capsulata photosynthetic antenna system have been distinguished by studying mutants lacking one or the other complex. In mutants containing only the light-harvesting I complex (LH-I), the absorption spectrum of the carotenoids is blue-shifted compared to wild type. Carotenoid absorption in mutants possessing only the light-harvesing II complex (LH-II) complex is red-shifted. The circular dichroism spectrum of carotenoids in each complex is also distinctive. Although carotenoids in each complex function with approximately the same efficiency in harvesting and transmitting light energy for photosynethesis, only the carotenoids associated with LH-II undergo an electrochromic bandshift upon generation of a transmembrane potential. These observations are interpreted to indicate that both the orientation of carotenoid molecules with respect to the plane of the membrane, and the immediate electrochemical environment of these molecules differ in the two light-harvesting complexes.  相似文献   

9.
《Inorganica chimica acta》1988,141(2):305-308
Lanthanide methanesulfonate (MS) 3-picoline N-oxide (3-picNO) complexes, with general formula [Ln(MS)3(3-picNO)2] (Ln LaYb, Y) present a non-electrolyte behavior in methanol, forming only one isomorphous series. The ligand is bonded through the oxygen, the MS ion being probably bidentate coordinated according to the IR data. From the electronic absorption spectra of the neodymium compound, the nephelauxetic and Sinha's parameters, covalent factor and the oscillator strength in solution were calculated and interpreted. The fluorescence spectrum of the europium complex was interpreted in terms of a C3v symmetry, with the geometry of a bicapped trigonal prism. The crystal-field parameters (Bkq) were also calculated.  相似文献   

10.
Nuclear scaffold attachment sites in the human globin gene complexes.   总被引:27,自引:2,他引:27       下载免费PDF全文
In an analysis of a 90-kb region around the human beta-globin gene complex we have identified at least eight sites of attachment to the nuclear scaffold (SARs). While these have many potential functions, there appears to be a particular association with sequences important in the regulation of the complex. Two SARs are close to the known enhancer-like elements of the beta-globin gene. SARs flanking the complex co-habit with the boundaries of the putative beta-like globin gene regulatory domain. In contrast, we have detected no SARs within a 140-kb region of the human alpha-globin gene complex. If SARs play a role in the regulation of gene expression then this structural difference would imply a difference in the regulation of the two complexes.  相似文献   

11.
Gamma-tubulin is as ubiquitous in eukaryotes as alpha- and beta-tubulin. Rather than forming part of the microtubule wall, however, gamma-tubulin is involved in microtubule nucleation. Although gamma-tubulin concentrates at microtubule-organizing centers, it also exists in a cytoplasmic complex whose size and complexity depends on the organism and cell type. In the past year, progress in understanding the functions of gamma-tubulin was made on two fronts: identifying the proteins that interact with gamma-tubulin and identifying the proteins that interact with the gamma-tubulin complex to tether it to the microtubule-organizing center.  相似文献   

12.
It is now widely accepted that, besides their well-established function in O(2) transport, hemoglobin and myoglobin also undergo several redox reactions aimed to scavenge toxic free radicals and reactive oxygen and nitrogen species. At least some of these reactions are believed to play an important physiological role in the defense against oxidative stress. This aspect is exemplified by the recently discovered neuroglobin, a globin expressed in the brain. Rather than being considerably involved in reversible O(2) binding, neuroglobin is likely to undergo redox reactions to protect neurons against oxidative and potentially pathogenic pathways, as those operating after episodes of tissue hypoxia or ischemia. A major part of the cellular damage occurring under such conditions has been ascribed to formation of peroxynitrite, that originates from the reaction between two biologically important free radicals, nitric oxide (NO ) and superoxide. Here we review the current knowledge of the reactions of different forms of hemoglobin, myoglobin, and neuroglobin with peroxynitrite and discuss their physiological role on the basis of measured rate constants and on the probability of occurrence of these reactions in vivo.  相似文献   

13.
The efficiency of PAMAM dendrimer-mediated DNA transfer can be improved by the addition of substituted beta-cyclodextrins (beta-CDs) as formulation excipients. In vitro CAT expression increased approximately 200-fold when dendrimer/DNA/beta-CD formulations were applied on the surface of collagen membranes. The inclusion of beta-CD into the formulations resulted in particles that were smaller and more evenly distributed on the surface of the solid support. The average size of the complex formed at 50 microg/ml and at charge ratio of 1 decreased from 156 nm to 5.8 nm and 21.2 nm in 0.025-0.1% w/vol beta-CDs. Sulfonated beta-CDs bind to dendrimer and in the increased concentration may displace DNA in the dendrimer/DNA complex. High concentrations of amphoteric beta-CD do not dissociate dendrimer/DNA complexes; however, they may decrease their ability to transfect cells. At the optimized formulations the surface-modified beta-CDs may enhance solid support-based transfection in vitro, through modification of dendrimer/DNA complex composition and improved surface distribution.  相似文献   

14.
15.
As part of a long-term study of the substitution reactions of piano-stool type cyclopentadienylmetal carbonyl complexes, several new methylcyclopentadienylmolybdenum compounds have been prepared and characterized by methods including IR spectroscopy, electrospray ionization mass spectrometry and X-ray crystallography. The complexes reported here include [{Cp′Mo(CO)3}2I]BPh4, cis-Cp′Mo(CO)2(PPh3)I and [Cp′Mo(CO)3(CH3CN)]BF4 (Cp′ = η5-C5H4CH3). In addition to their syntheses, comparisons are made between their IR spectroscopic and X-ray crystal structure data and those of similar complexes.  相似文献   

16.
17.
Spectral characteristics of aminoacyl-tRNA-synthetases (ARSases) isolated from muscles of normal rabbits and of those fasted for a long time were studied by the methods of fluorescence and differential spectroscopy. Fluorescence spectra and differential absorption spectra of the compared proteins evidenced for more hydrophobic surrounding of tryptophanyls and their less accessibility for Cs+ ions in proteins of fasted animals. Interaction of aspartyl- and valyl-tRNA-synthetases from muscles of normal and long-fasted rabbits with substrates is accompanied by the essential quenching of tryptophan fluorescence of ARSases. Equilibrium constants of substrate binding calculated from the fluorescence quenching curves are higher for specific amino acids than for non-specific ones. The effect of a long-wave shift of fluorescence spectra under marginal excitation of tryptophan residues was used to determine structural differences of enzymes in norm and under fasting and to find their structural peculiarities during formation of aminoacyl adenylate. Aminoacyl-tRNA-synthetases (ARSases) are key enzymes of the protein biosynthesis. High specificity of their interaction with substrates is the basis for the accuracy of genetic information implementation, namely translation of the genetic code. Molecular mechanisms of substrates "recognition" by ARSases are the objects of great attention of researchers.  相似文献   

18.
Several novel structures of legume lectins have led to a thorough understanding of monosaccharide and oligosaccharide specificity, to the determination of novel and surprising quaternary structures and, most importantly, to the structural identification of the binding site for adenine and plant hormones. This deepening of our understanding of the structure/function relationships among the legume lectins is paralleled by advances in two other plant lectin families - the monocot lectins and the jacalin family. As the number of available crystal structures increases, more parallels between plant and animal lectins become apparent.  相似文献   

19.
20.
C E Cooper  E Odell 《FEBS letters》1992,314(1):58-60
EPR (electron paramagnetic resonance) and optical spectroscopy show that human neutrophil myeloperoxidase is converted from ferric high-spin to low-spin by the addition of nitrite. The Soret peak shifts from 429 to 447 nm and new peaks appear in the visible region at 573 and 627 nm; the EPR g-values change from 6.84, 5.02, 1.95 to 2.55, 2.31, 1.82. Small differences are seen in the EPR (but, not optical) spectra of myeloperoxidase isoenzyme I compared to isoenzymes II and III. The reaction with nitrite is detectable by EPR in intact neutrophils and is thus a possible in vivo monitor of NO/nitrite production by these cells.  相似文献   

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