Biomedical subjects

G Henkel

Publications and source records attributed to G Henkel.

At least 19 recordsLinked to original sources

PubMed2001

Synthesis and properties of the tetrakis(trifluoromethyl)borate anion, [b(CF3)4]-: structure determination of Cs[B(CF3)4] by single-crystal X-ray diffraction.

Salts of the tetrakis(trifluoromethyl)borate anion, M[B(CF3)4], M=Li, K, Cs, Ag, have been prepared by two different routes for the first time. The colorless compounds are thermally stable up to 425 C (Cs salt) and soluble in anhydrous HF, water, and most organic solvents. Single crystals of Cs[B(CF3)4] were grown from diethyl ether by diffusion of CH2Cl2 vapor into the solution. The molecular structure was obtained by single-crystal X-ray diffraction. Crystal data: rhombohedral space group R3m (no. 160); a =7.883(1), c=13.847(4) A: V=748.2 A3; Z=3; T=150K; R1=0.0118, wR2=0.0290. The internal bond parameters of the [B(CF3)4] ion were compared to those of the C(CF3)4 molecule. Due to a disorder of the anions in the cesium salt, it is not possible to distinguish between T and Td symmetry by X-ray diffraction experiments alone. However, a comprehensive IR and Raman study demonstrated that in the potassium and cesium salt as well as in aqueous solution, the anion exhibits T symmetry with all CF3 groups rotated off the staggered position required for Td symmetry. The vibrational study is supported by DFT calculations, which provide, in addition to the equilibrium structure and vibrational wavenumbers, estimates of IR and Raman band intensities. The anion is resistant against strong oxidizing (e.g., F2) as well as reducing agents (e.g., Na) and is not affected by nucleophiles like C2H5O or electrophiles such as H3O+. It is very weakly coordinating, as demonstrated by the low-equilibrium CO pressure over the [Ag(CO)x][B(CF3)4] (x=1, 2) co-adducts and the formation of [Ag(CO)x][B(CF3)4] (x=3,4) at higher CO pressure. The 11B, 13C, and 19F NMR data as well as the structural parameters of the anion are compared with those for other borates containing F, CN, and CF3 ligands.

Journal Article↗

PubMed2001

Tetrameric fluorophosphazene, (NPF(2))(4), planar or puckered?

The results obtained in a comprehensive experimental study on the redetermination of the structure of N(4)P(4)F(8) with single-crystal X-ray diffraction, gas electron diffraction (GED), and differential scanning calorimetry (DSC) establish clearly that, in contrast to the previous report, the eight-membered heterocycle is not planar. Above the phase transition temperature of -74 degrees C, the ring appears pseudoplanar. However, the N(4)P(4) ring is disordered and is puckered above the phase transition when the disorder is modeled correctly. Below the phase transition the ring clearly resembles that of the saddle (K form) of N(4)P(4)Cl(8). The unit cell of the low-temperature phase is derived from that of the higher temperature phase by doubling the c-axis and removing one-half of the symmetry elements. Full structure optimizations were performed at the HF/6-31G and B3LYP/6-31G levels and fully support the experimental diffraction data.

Journal Article↗

PubMed2001

The Fe-only nitrogenase from Rhodobacter capsulatus: identification of the cofactor, an unusual, high-nuclearity iron-sulfur cluster, by Fe K-edge EXAFS and 57Fe Mössbauer spectroscopy.

Samples of the dithionite-reduced FeFe protein (the dinitrogenase component of the Fe-only nitrogenase) from Rhodobacter capsulatus have been investigated by 57Fe Mössbauer spectroscopy and by Fe and Zn EXAFS as well as XANES spectroscopy. The analyses were performed on the basis of data known for the FeMo cofactor and the P cluster of Mo nitrogenases. The prominent Fourier transform peaks of the Fe K-edge spectrum are assigned to Fe-S and Fe-Fe interactions at distances of 2.29 A and 2.63 A, respectively. A significant contribution to the Fe EXAFS must be assigned to an Fe backscatterer shell at 3.68 A, which is an unprecedented feature of the trigonal prismatic arrangement of iron atoms found in the FeMo cofactor of nitrogenase MoFe protein crystal structures. Additional Fe...Fe interactions at 2.92 A and 4.05 A clearly indicate that the principal geometry of the P cluster is also conserved. Mössbauer spectra of 57Fe-enriched FeFe protein preparations were recorded at 77 K (20 mT) and 4.2 K (20 mT, 6.2 T), whereby the 4.2 K high-field spectrum clearly demonstrates that the cofactor of the Fe-only nitrogenase (FeFe cofactor) is diamagnetic in the dithionite-reduced ("as isolated") state. The evaluation of the 77 K spectrum is in agreement with the assumption that this cofactor contains eight Fe atoms. In the literature, several genetic and biochemical lines of evidence are presented pointing to a significant structural similarity of the FeFe, the FeMo and and the FeV cofactors. The data reported here provide the first spectroscopic evidence for a structural homology of the FeFe cofactor to the heterometal-containing cofactors, thus substantiating that the FeFe cofactor is the largest iron-sulfur cluster so far found in nature.

Ferredoxins↗

PubMed2000

An intron transcriptional enhancer element regulates IL-4 gene locus accessibility in mast cells.

The cell type-specific expression of a gene is dependent on developmentally regulated modifications in chromatin structure that allow accessibility of basal and inducible transcription factors. In this study, we demonstrate that a cis-acting element in the second intron of the murine IL-4 gene has a dual function in regulating transcription in mast cells as well as chromatin accessibility of the IL-4 gene locus through its influence on the methylation state of the gene. Previous studies have shown that mast cell-restricted transcription factors GATA-1/2 and PU.1 associate with the intron element and regulate its activity. In this study, we use DNase I footprinting and mutational analyses to identify two additional sites that contribute to the element's ability to enhance transcription. One of these sites associates preferentially with STAT5a and STAT5b. We also demonstrate that deletion of the element or mutation of the GATA binding site in the context of a stably integrated IL-4 genomic construct prevents maintenance of a demethylated locus in IL-4-producing mast cells. These data indicate that, analogous to Ig and TCR intron regulatory elements, the intron enhancer has an essential role in maintaining developmentally regulated demethylation at the IL-4 gene locus. In addition, they indicate that members of the GATA family of transcription factors likely play an important role in these processes.

Animals↗

PubMed1999

C(6)F(5)XeCl and

Xenon(II) chlorine compounds can be obtained as the isolable organo derivatives C(6)F(5)XeCl and [(C(6)F(5)Xe)(2)Cl][AsF(6)] (whose cation is depicted) in 85 and 91 % yield, respectively. These compounds decompose vigorously at 36 degrees C and 100 degrees C, respectively, leading to the formation of C(6)F(5)Cl and Xe gas and of C(6)F(5)Cl, C(6)F(6), and [C(6)F(5)Xe][AsF(6)], respectively.

Journal Article↗

PubMed1996

Nuclear factor of activated T cells is associated with a mast cell interleukin 4 transcription complex.

Interleukin 4 (IL-4), an immunoregulatory cytokine, is produced only by a subset of activated T cells and cells of the mast cell-basophil lineage. The production of IL-4 by mast cells likely represents a significant source of this protein in local immune-inflammatory responses in the skin, brain, gastrointestinal, and respiratory tracts, in which mast cells are prevalent. In the present study, the cis- and trans-acting elements that control inducible mast cell IL-4 gene transcription were examined and compared with those that function in T cells. We demonstrate that, as in T cells, sequences between bp -87 and -70 are critical for protein association and activation-dependent gene transcription and that this region (termed the activation-responsive element region) is the target of an inducible, cyclosporin A-sensitive, DNA-protein interaction. When assessed by electrophoretic mobility shift assays and UV cross-linking analyses, multiple proteins in both T- and mast cell nuclear extracts associate with the activation-responsive element in vitro, and some of these appear identical. However, distinct proteins are associated with each of the complexes as well. AP-1 family members are unique to the T-cell-stimulation-dependent complex, whereas mast cell complexes contain factors that are reactive with anti-nuclear factor of activated T cells p (NF-ATp) and anti-NF-ATc antibodies but have distinct molecular masses compared with those of T-cell-derived NF-AT. Furthermore, an anti-NF-ATp-reactive factor with a molecular mass of approximately 41 kDa is present in the nuclei of unstimulated cells and binds independently of cell activation, unlike the previously described NF-AT family members. These data support the idea that there are uniquely regulated, cell lineage-specific transcription factors related to T-cell-derived NF-AT that mediate inducible IL-4 transcription in mast cells. These differences likely reflect the distinct cell surface signaling requirements for IL-4 production in T and mast cells.

Animals↗

PubMed1996

Ras-mediated phosphorylation of a conserved threonine residue enhances the transactivation activities of c-Ets1 and c-Ets2.

The Ras oncogene products regulate the expression of genes in transformed cells, and members of the Ets family of transcription factors have been implicated in this process. To determine which Ets factors are the targets of Ras signaling pathways, the abilities of several Ets factors to activate Ras-responsive enhancer (RRE) reporters in the presence of oncogenic Ras were examined. In transient transfection assay, reporters containing RREs composed of Ets-AP-1 binding sites could be activated 30-fold in NIH 3T3 fibroblasts and 80-fold in the macrophage-like line RAW264 by the combination of Ets1 or Ets2 and Ras but not by several other Ets factors that were tested in the assay. Ets2 and Ras also superactivated an RRE composed of Ets-Ets binding sites, but the Ets-responsive promoter of the c-fms gene was not superactivated. Mutation of a threonine residue to alanine in the conserved amino-terminal regions of Ets1 and Ets2 (threonine 38 and threonine 72, respectively) abrogated the ability of each of these proteins to superactivate reporter gene expression. Phosphoamino acid analysis of radiolabeled Ets2 revealed that Ras induced normally absent threonine-specific phosphorylation of the protein. The Ras-dependent increase in threonine phosphorylation was not observed in Ets2 proteins that had the conserved threonine 72 residue mutated to alanine or serine. These data indicate that Ets1 and Ets2 are specific nuclear targets of Ras signaling events and that phosphorylation of a conserved threonine residue is a necessary molecular component of Ras-mediated activation of these transcription factors.

Amino Acid Sequence↗

PubMed1994

PU.1 and GATA: components of a mast cell-specific interleukin 4 intronic enhancer.

Interleukin 4 (IL-4), a critical immunoregulatory cytokine, is produced by a subset of T lymphocytes and cells of the mast cell/basophil lineage. There are cell-specific differences in the regulatory elements that control IL-4 transcription in these two cell types. A 683-bp Bgl II fragment, located within the second intron of the murine IL-4 gene, was previously shown to exhibit mast cell-specific enhancer activity. To define critical cis-acting elements that regulate this enhancer, a series of deletions from the 5' and 3' ends of the Bgl II fragment were generated. Their effect on enhancer activity was assessed in IL-4-producing mast cell lines in transient transfection assays. Two functionally independent subregions, E1 and E2, were defined in this analysis. Both are required for full enhancer activity. Sequences identical to previously defined DNA-binding sites for SP1 and GATA are present within E1, and an ets binding site is located within E2. Although mutation of the SP1 sites had no effect on enhancer function, alteration of either the GATA or ets site reduced enhancer activity by 50-60%. Proteins that associate with the IL-4 intronic GATA and ets sites were detected in mast cell nuclear extracts by mobility-shift assays. Specific antibodies identified these factors as GATA-1 and GATA-2 and the ets family member PU.1. GATA-1, GATA-2, and PU.1 exhibit cell-specific expression, suggesting that these proteins play a critical role in the lineage-restricted activity of the IL-4 intronic enhancer in mast cells.

Animals↗

PubMed1994

Mössbauer and magnetic susceptibility studies on iron(II) metallothionein from rabbit liver. Evidence for the existence of an unusual type of [M3(CysS)9]3- cluster.

The magnetic properties of the Fe(II)-binding sites in Fe(II)7-metallothionein (MT) have been studied using Mössbauer spectroscopy and magnetic-susceptibility measurements. In agreement our previous results, simulation of the Mössbauer spectra showed the presence of paramagnetic and diamagnetic subspectra in the ratio 3:4. By comparison with Mössbauer spectra of the inorganic adamantane-like (Et4N)2[Fe4(SEt)10] model compound, the diamagnetic component in Fe(II)7-MT has been assigned to a four-metal cluster in which there is antiferromagnetic coupling between the high-spin Fe(II) ions. It is suggested that the organization of this cluster is similar to that determined in the three-dimensional structure of the protein, containing diamagnetic Zn(II) and/or Cd(II) ions. From magnetic-susceptibility studies, an average magnetic moment of approximately 8.5 microB was obtained for the three remaining bound Fe(II) ions, responsible for the paramagnetic component observed in the Mössbauer studies. This value is slightly lower than that for three completely uncoupled Fe(II) ions, suggesting the existence of a three-metal cluster within which there is weak exchange coupling between adjacent Fe(II) ions. The spin-Hamiltonian formalism including, besides zero-field and Zeeman interaction, also exchange interaction among the three Fe(II) ions in the three-metal cluster, H = -J12 (S1.S2)-J23 (S2.S3)-J13 (S1.S3), was applied to simulate both magnetic-Mössbauer and magnetic-susceptibility data. Reasonable fits were achieved only with values magnitude of J12 = magnitude of J23 = magnitude of J13 = magnitude of J < 1 cm-1. Such a situation could not be reconciled with the chair-like geometry of the [M3(CysS)9]3- cluster determined with paramagnetic metal ions, where significantly stronger coupling would be anticipated (magnitude of J = 50-70 cm-1). However, modest exchange-coupling properties have been reported for a number of crystallographically characterized trinuclear [Fe3(SR)3X6]3- clusters (X = Cl, Br; R = Phe, p-tolyl, 2,6-Me2C6H3) distinguished by the preferential formation of a planar Fe3(mu 2-SR)3 ring [Whitener, M. A., Bashkin, J. A., Hagen, K. S., Girerd, J.-J., Gamp, E. Edelstein, N. & Holm, R. H. (1986) J. Amer. Chem. Soc. 108, 5607-5620]. It is therefore more likely that a pseudo-planar geometry rather than a chair-like geometry is present in the Fe3 cluster of Fe(II)7-MT. This would represent the first example of structural differences on binding divalent metal ions to this protein.

Adamantane↗

PubMed1994

Dimerisation of levonorgestrel in solid state ultraviolet light irradiation.

UV-irradiation of levonorgestrel (1) in the crystalline state under a nitrogen atmosphere yielded its dimer, [17 alpha[1R-(1 alpha,2 beta,4a beta,4b alpha,10a alpha)]]-13-ethyl-17- [4- (2-ethyl-1,2,3,4a,4b,5,6,7,9,10,10a-dodecahydro-7-oxo-1-phenant renyl)-1- methylen-2-oxo-butoxy]-18,19-dinorpregna-4-en-20-in-3-one(3) , as the principal photoproduct. It was characterized from its spectral and analytical data. The single crystal X-ray crystallographic data of 1 indicated the possibility of its photochemical dimerisation.

Crystallography, X-Ray↗

PubMed1992

A DNase I-hypersensitive site in the second intron of the murine IL-4 gene defines a mast cell-specific enhancer.

IL-4 is a potent immunoregulatory cytokine that exhibits extremely diverse effects on a number of target cells. Although IL-4 was originally described as a T cell-derived product, it is evident that cells of the basophil/mast cell lineage are also an important source of this cytokine. Based on their different tissue distribution, mast cell and T cell-derived IL-4 may have distinct effects on local immune responses. The physiologic production of IL-4 appears to be tightly regulated because most T and mast cells require activation to express significant levels of IL-4. In contrast, a majority of murine transformed mast cell lines constitutively express relatively high levels of IL-4. In this study, transformed mast cell lines were used as models to define cis acting sequences that regulate mast cell IL-4 transcription. Chloramphenicol acetyltransferase reporter gene constructs containing 6.3 kb of 5' IL-4 flanking sequence direct relatively low chloramphenicol acetyltransferase expression in these cells. These results indicated that additional sequences may be important in stimulating transcriptional activity of the IL-4 gene. Using DNAse I hypersensitive site analysis to define other potential IL-4 transcriptional regulatory regions, two sites were identified in the murine IL-4 gene that appear to be unique to IL-4 expressing transformed mast cells. One site defines an intronic sequence that exhibits prototypic enhancer activity in several independently derived transformed mast cell lines. This enhancer is also active in stimulated, non-transformed mast cells but not stimulated EL-4 T cells. Taken together, these data indicate that the IL-4 intronic sequence contains a mast cell specific enhancer that plays an essential role in the unregulated expression of IL-4 in transformed mast cells and may also be important in the inducible expression of IL-4 in normal mast cells.

Animals↗

PubMed1989

Extended X-ray absorption fine structure (EXAFS) investigations of model compounds for zinc enzymes.

A test of the ability of extended X-ray absorption fine structure (EXAFS) to determine structural information with specific reference to zinc sites in enzymes has been made. X-ray absorption spectra of 18 compounds of zinc have been measured and the nearest-neighbour scattering has been interpreted using a Fourier transform and an ab initio technique. Empirical Zn-N, Zn-O, Zn-S and Zn-Cl amplitude and phase functions have been extracted from Zn(C3H4N2)4(ClO4)2, ZnO, Zn(S2COC2H5)2 and [N(CH3)4]2[ZnCl4], respectively and tabulated as a function of the wavevector with respect to 9660.0 eV X-ray energy. These amplitude and phase functions were then tested with respect to the other 14 compounds. For a single species of atoms in the first coordination shell the interatomic distances can be established to +/- 0.5 pm (+/- 5 x 10(-3) A) whilst when mixed shells exist errors in distances are +/-4 pm (+/- 40 x 10(-3) A). Coordination numbers are given to +/- 16% for the single species case a and +/- 25% for the mixed coordination case. Using the theoretical amplitude and phase functions of McKale et al. [(1988) J. Am. Chem. Soc. 110, 3763-3768] the deduced distances are systematically too small by an average of 0.6 pm (6 x 10(-3) A). The errors in the coordination numbers are 18%.

Enzymes↗

PubMed1987

[Behavior in disability assessment of uncomplicated duodenal ulcer--a study].

There is internationally no standardized therapy of the uncomplicated duodenal ulcer, including the inability to work. In order to obtain a representative behaviour concerning the duration of the inability to work prescribed by specialists for general medicine, internal medicine and surgery, an interrogation was performed. An evaluation of 729 questionnaires shows the following tendency: 1. The younger the attending physician is the longer is the time of inability to work prescribed and the more frequent such a certificate is given. 2. General practitioners in rural districts on an average prescribe a longer time of inability to work. 3. The higher is the qualification of the specialist for internal medicine the shorter is the duration of inability to work attested. 4. In the assessment of the duration of the inability to work the attending physicians increasingly accommodate themselves rather to the symptoms than to the radiological or to the endoscopic control of healing.

Attitude of Health Personnel↗

PubMed1987