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Biomedical subjects

M Fischer

Publications and source records attributed to M Fischer.

At least 145 records · Page 8Linked to original sources
PubMed2000

Zinc plays a key role in human and bacterial GTP cyclohydrolase I.

The crystal structure of recombinant human GTP cyclohydrolase I was solved by Patterson search methods by using the coordinates of the Escherichia coli enzyme as a model. The human as well as bacterial enzyme were shown to contain an essential zinc ion coordinated to a His side chain and two thiol groups in each active site of the homodecameric enzymes that had escaped detection during earlier studies of the E. coli enzyme. The zinc ion is proposed to generate a hydroxyl nucleophile for attack of imidazole ring carbon atom eight of the substrate, GTP. It may also be involved in the hydrolytic release of formate from the intermediate, 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone 5'-triphosphate, and in the consecutive Amadori rearrangement of the ribosyl moiety.

Amino Acid Sequence↗
PubMed2000

Piracetam versus acetylsalicylic acid in secondary stroke prophylaxis. A double-blind, randomized, parallel group, 2 year follow-up study.

Piracetam has been shown to inhibit platelet aggregation. Therefore, we performed a double-blind, randomized, parallel group study to compare the efficacy of daily 1600 mg piracetam t.i.d. vs. 200 mg acetylsalicylic acid (ASA) t.i.d. in secondary stroke prophylaxis. 563 patients after stroke as confirmed by computed tomography (CT) or magnetic resonance imaging (MRI) were enrolled and received either piracetam or ASA during a 2 year follow-up period. The primary endpoint was the rate of stroke, transient ischaemic attack (TIA), or death from vascular cause. The secondary endpoint was the rate of adverse events leading to a premature discontinuation of the study medication. Patients were visited at home every 3 months and were examined in hospital after 1 and 2 years. At every visit, the platelet function was evaluated. No significant difference and no significant equivalence could be shown for the primary endpoint between the piracetam and the ASA group both in the intention-to-treat and in the per-protocol analysis. However, there was a not significant trend in favor of ASA (11.7 vs. 15.2%). After excluding those patients who did not respond to antiplatelet medication in vitro, however, piracetam and ASA were equivalent in secondary stroke prophylaxis (stroke, TIA, or vascular death 10.1% in the piracetam group vs. 9.7% in the ASA group). Piracetam was significantly superior to ASA in the secondary endpoint (P=0.0039). The data suggest that the overall efficacy of piracetam in secondary stroke prophylaxis is not as good as that of ASA but that piracetam is better tolerated. However, our data furthermore show that nonresponders to pharmacological inhibition of platelet function are more frequent under piracetam therapy and that they may influence the results of large studies on secondary prophylaxis in vascular diseases.

Aspirin↗
PubMed2000

Platelet glycoprotein expression in patients with myelodysplastic syndrome.

Myelodysplastic syndromes (MDS) are characterized by a haematopoetic insufficiency that can lead to acute leukemia. A multistep pathogenesis caused by a clonal stem cell defect affecting several differentiation pathways has been proposed for MDS. Contrary to the better characterized alteration of lymphoid and myeloid differentiation, defects in thrombocytopoesis in MDS remain less clear. In the present study, we analyzed the expression of platelet glycoprotein (GP) Ia/IIa, IIb/IIIa, Ib/IX, and IV in 21 MDS patients (12 RA, 2 RARS, 4 RAEB, 1 RAEB-T, 2 CMML) and healthy controls by flowcytometric analysis and quantitation of platelet GP RNA using fluorescence-based PCR. We observed a reduced cell surface expression of GPIb (p<0.01) and GPIIb/IIIa (p<0.01), while GPIa/IIa and GPIV expression was only marginally different between patients and controls. In contrast, there was a two-fold increase of platelet GPIb and GPIIb RNA and a three-fold increase of GPIV RNA among MDS patients. Increased levels of platelet GPIb and GPIIb RNA were significantly more prominent among patients with RAEB(-T)/CMML (p<0. 05) in comparison to patients with RA/RARS. In conclusion, we demonstrate alterations in the cell surface expression and RNA content of platelet GPs in MDS patients. These data are consistent with dysmegakaryocytopoiesis and a defect in thrombocytopoiesis among MDS patients resulting from the clonal stem cell defect in MDS.

Adult↗
PubMed2000

Collective singlet excitations and evolution of raman spectral weights in the 2D spin dimer compound SrCu2(BO3)(2)

Raman light scattering of the two-dimensional quantum spin system SrCu2(BO3)(2) shows a rich structure in the magnetic excitation spectrum, including several well-defined bound state modes at low temperature, and a scattering continuum and quasielastic light scattering contributions at high temperature. The key to the understanding of the unique features of SrCu2(BO3)(2) is the presence of strong interactions between well-localized triplet excitations in the network of orthogonal spin dimers realized in this compound.

Journal Article↗
PubMed2000

Effects of calcium on the discharge pattern of primary and secondary endings of isolated cat muscle spindles recorded under a ramp-and-hold stretch.

The impulse activity of muscle spindles isolated from the cat tenuissimus muscle was investigated under varying concentrations of external calcium (Ca(2+)). The outer capsule of the muscle spindle represents an effective diffusion barrier for Ca(2+) ions since activity changes were strong and rapid only if the capsule was partly removed from the sensory region of the receptor. The impulse activity of both primary and secondary muscle spindle endings was lowered by an increase in the external Ca(2+) concentration from 1.8 mM (normal Ringer's solution) to 2.7 mM and raised by a decrease in the Ca(2+) concentration from 1.8 to 0.9 mM. Primary endings were generally more strongly affected than secondary endings. With primary endings the firing rate changed by 23-52% when the external Ca(2+) concentration was altered by 0.9 mM. With secondary endings the discharge frequency changed by 15-24%. The afferent discharge patterns were obtained under repetitive ramp-and-hold stretches and were analyzed with regard to influences of external Ca(2+) ions on the static and dynamic components of the endings' responses. The stretch sensitivity and the adaptive response of both types of ending increased in the low Ca(2+) solution and decreased in the high Ca(2+) solution, but a specific effect on a single component of the responses to stretch was not observed. These findings indicate an overall change in excitability when the external Ca(2+) concentration was varied. The mechanical properties of the receptor were probably not affected since changes in the Ca(2+) concentration did not elicit a contraction or relaxation of the intrafusal muscle fibers. On the one hand, the observed effects can be explained according to the surface potential theory by an indirect influence of extracellular Ca(2+) ions on ion channels of the sensory nerve terminals, with Ca(2+) ions binding to negative charged sites at the endings' outer membrane. On the other hand, the results are consistent with the supposition that Ca(2+) ions act directly on ion channels of the sensory membrane of muscle spindle endings.

Adaptation, Physiological↗
PubMed2000

Residual HIV-RNA levels persist for up to 2.5 years in peripheral blood mononuclear cells of patients on potent antiretroviral therapy.

The long-term response of 10 asymptomatic, antiretroviral therapy-naive HIV-1-infected patients to potent combination antiretroviral therapy was characterized by monitoring levels of HIV-1 RNA in plasma, peripheral blood mononuclear cells (PBMC), and lymphoid tissue using highly sensitive HIV-1 RNA assays. Although plasma viral loads were continuously suppressed to levels below 50 HIV-1 RNA copies/ml for up to 2.5 years (60-128 weeks), HIV-1 RNA was still detectable at very low levels (1 to 49 HIV-1 RNA copies/ml) in 25% of the samples. In corresponding PBMC specimens, residual HIV-RNA was detectable in as much as 91% of samples tested (1 to 420 HIV-1 RNA copies/microg total RNA). Similarly, HIV-1 RNA levels in lymphoid tissue also remained detectable at a high frequency (86%). A highly significant correlation was demonstrated between therapy-induced change in PBMC HIV-1 RNA levels and change in plasma HIV-1 RNA levels (r2 = 0.69; p = 0.003). These findings support the concept that measurement of HIV-1 RNA in the easily accessible PBMC compartment is relevant for evaluating the potency of current and future antiretroviral therapies.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Biosynthesis of terpenoids: 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase from tomato.

The putative catalytic domain (residues 81-401) of a predicted tomato protein with similarity to 4-diphosphocytidyl-2-C-methyl-d-erythritol kinase of Escherichia coli was expressed in a recombinant E. coli strain. The protein was purified to homogeneity and was shown to catalyze the phosphorylation of the position 2 hydroxy group of 4-diphosphocytidyl-2-C-methyl-d-erythritol at a rate of 33 micromol small middle dotmg(-1) small middle dotmin(-1). The structure of the reaction product, 4-diphosphocytidyl-2-C-methyl-d-erythritol 2-phosphate, was established by NMR spectroscopy. Divalent metal ions, preferably Mg(2+), are required for activity. Neither the tomato enzyme nor the E. coli ortholog catalyzes the phosphorylation of isopentenyl monophosphate.

Amino Acid Sequence↗
PubMed2000

The atomic structure of pentameric lumazine synthase from Saccharomyces cerevisiae at 1.85 A resolution reveals the binding mode of a phosphonate intermediate analogue.

Lumazine synthase of Saccharomyces cerevisiae is a homopentamer with a molecular weight of 90 kDa. Crystals of the recombinant enzyme with a size of up to 1.6 mm were obtained. The space group is P4(1)2(1)2 with lattice dimensions 82.9 A x 82.9 A x 300.2 A. X-ray diffraction data collected under cryogenic conditions were complete to 1.85 A resolution. The structure of the enzyme in complex with the intermediate analogue, 5-(6-D-ribitylamino-2,4-dihydroxypyrimidine-5-yl)-1-pentyl-p hosphonic acid was solved via molecular replacement using the structure of the Bacillus subtilis enzyme as search model and was refined to a final R-factor of 19.8% (Rfree: 22.5%). The conformation of the active site ligand of the enzyme mimicks that of the Schiff base intermediate of the enzyme-catalyzed reaction. The data enable the reconstruction of the reactant topology during the early steps of the catalytic reaction. Structural determinants, which are likely to be responsible for the inability of the S. cerevisiae enzyme to form icosahedral capsids, will be discussed.

Amino Acid Sequence↗
PubMed2000

Localization of a short-term memory in Drosophila.

Memories are thought to be due to lasting synaptic modifications in the brain. The search for memory traces has relied predominantly on determining regions that are necessary for the process. However, a more informative approach is to define the smallest sufficient set of brain structures. The rutabaga adenylyl cyclase, an enzyme that is ubiquitously expressed in the Drosophila brain and that mediates synaptic plasticity, is needed exclusively in the Kenyon cells of the mushroom bodies for a component of olfactory short-term memory. This demonstrates that synaptic plasticity in a small brain region can be sufficient for memory formation.

Adenylyl Cyclases↗
PubMed2000

Stripe conductivity in La1.775Sr0.225NiO4

We report Raman light-scattering and optical conductivity measurements on a single crystal of La1.775Sr0.225NiO4 which exhibits incommensurate charge-stripe order. The extra phonon peaks induced by stripe order can be understood in terms of the energies of phonons that occur at the charge-order wave vector Q(c). A strong Fano antiresonance for a Ni-O bond-stretching mode provides clear evidence for finite dynamical conductivity within the charge stripes.

Journal Article↗
PubMed2000

Fully synthetic human combinatorial antibody libraries (HuCAL) based on modular consensus frameworks and CDRs randomized with trinucleotides.

By analyzing the human antibody repertoire in terms of structure, amino acid sequence diversity and germline usage, we found that seven V(H) and seven V(L) (four Vkappa and three Vlambda) germline families cover more than 95 % of the human antibody diversity used. A consensus sequence was derived for each family and optimized for expression in Escherichia coli. In order to make all six complementarity determining regions (CDRs) accessible for diversification, the synthetic genes were designed to be modular and mutually compatible by introducing unique restriction endonuclease sites flanking the CDRs. Molecular modeling verified that all canonical classes were present. We could show that all master genes are expressed as soluble proteins in the periplasm of E. coli. A first set of antibody phage display libraries totalling 2x10(9) members was created after cloning the genes in all 49 combinations into a phagemid vector, itself devoid of the restriction sites in question. Diversity was created by replacing the V(H) and V(L) CDR3 regions of the master genes by CDR3 library cassettes, generated from mixed trinucleotides and biased towards natural human antibody CDR3 sequences. The sequencing of 257 members of the unselected libraries indicated that the frequency of correct and thus potentially functional sequences was 61 %. Selection experiments against many antigens yielded a diverse set of binders with high affinities. Due to the modular design of all master genes, either single binders or even pools of binders can now be rapidly optimized without knowledge of the particular sequence, using pre-built CDR cassette libraries. The small number of 49 master genes will allow future improvements to be incorporated quickly, and the separation of the frameworks may help in analyzing why nature has evolved these distinct subfamilies of antibody germline genes.

Amino Acid Sequence↗
PubMed2000

Effects of chlorobutanol on primary and secondary endings of isolated cat muscle spindles.

The effects of the preservative chlorobutanol on primary and secondary endings of muscle spindles isolated from the tenuissimus muscle of the cat were investigated in this study. Chlorobutanol was applied to the bathing solution in final concentrations of between 10 and 100 microg/ml. It induced a reversible and dose dependent decrease in the discharge frequency of both types of ending without any visible length change in the sensory region of the receptor. The initial activity, the peak dynamic discharge, the maximum static discharge value and the final static discharge value were evaluated from an ending's discharge pattern obtained during ramp-and-hold stretches. These four basic discharge frequencies decreased in parallel with increasing concentrations of chlorobutanol. Their sensitivities to chlorobutanol were similar (mean values: -0.11 to -0.29 imp/s per microg/ml chlorobutanol) and were independent of the amplitude of stretch. The dynamic response and the static response of both primary and secondary endings remained unchanged, indicating that the sensitivity of the spindle to stretch was not influenced by chlorobutanol. Chlorobutanol also reduced the discharge activity of the muscle spindle afferents during sinusoidal stretches. The amplitude of the receptor potential (AC component) remained unchanged under chlorobutanol. With the available recording technique it was not possible to measure slow shifts of the membrane potential. However, a hyperpolarization of the ending's membrane might explain why the afferent discharge frequency is reduced by chlorobutanol. The calcium dynamics of the spindle do not appear to be altered by CB, as the effect exerted on the afferent discharge by a change in the extracellular calcium concentration and a blockage of calcium channels was different from the CB effect. As the inhibitory effect of CB was reduced by ouabain, it is possible that CB activates the electrogenic Na/K pump or affects a mechanism that is closely related to the activity of the pump. The properties of the axonal membrane appear not to be altered, as chlorobutanol did not change the shape of action potentials.

Action Potentials↗
PubMed2000

The tumor-associated shift in immunoglobulin G1/G2 is expressed at the messenger RNA level of peripheral blood B lymphocytes in patients with gynecologic malignancies.

BACKGROUND: Previously, it could be demonstrated that human patients with malignant diseases of various tissues exhibited characteristic and highly significant changes in the serum patterns of immunoglobulin (Ig)G subclasses, consisting of a decrease in IgG1 and an increase in IgG2 relative to total IgG. The aim of the current study was to determine whether this phenomenon was detectable at the level of IgG-producing B lymphocytes. METHODS: Using a competitive reverse transcriptase polymerase chain reaction specific to IgG1 and IgG2, the gene expression of these 2 IgG subclasses in peripheral B cells from 10 patients with carcinomas of various sites within the female reproductive tract and 10 healthy controls was quantitatively determined, in parallel with the concentrations of the respective serum proteins. RESULTS: Absolute levels of IgG subclass messenger ribonucleic acid (mRNA) showed a slight but not significant decrease in IgG1 and an increase in IgG2 in patients with gynecologic malignancies. However, the ratio of IgG1 to IgG2 expression showed a highly significant (P < 0.001) decrease in tumor patients compared with healthy controls, and corresponded to the change in the ratio of IgG1 to IgG2 serum proteins. CONCLUSIONS: These data suggest that the shifts in the serum patterns of IgG1 and IgG2 observed in patients with gynecologic malignancies are due to irregular biosynthesis of these IgG subclasses at the B-cell level.

B-Lymphocytes↗
PubMed2000

Effects of early antiretroviral treatment on HIV-1 RNA in blood and lymphoid tissue: a randomized trial of double versus triple therapy. Swiss HIV Cohort Study.

To assess the effects of early initiation of antiretroviral therapy on cell-free and cell-associated viral load in blood and lymphoid tissue, we performed a randomized, open-label, multicenter trial comparing a double (zidovudine + lamivudine) and triple (zidovudine + lamivudine + ritonavir) drug combination in treatment-naive, asymptomatic patients with CD4 counts >400 cells/microl. HIV-1 RNA was measured in plasma, peripheral blood mononuclear cells, and sequential tonsil or lymph node biopsies (27 patients); the study follow-up was 2 years. Among 42 randomized patients, the proportion with plasma HIV-1 RNA <50 copies/ml was 16% and 74% at week 24 (p<.001) in those randomized to double and triple therapy, respectively, necessitating frequent treatment intensification in the double arm. After a rapid decline within 4 weeks in both arms, cell-associated HIV-1 RNA decreased further only in those patients with sustained suppression of plasma viral load, but remained almost always detectable at low levels, indicating persisting transcription of viral RNA. CD4 counts increased by 200 to 250 cells/microl at week 96 in both arms without significant differences (intent-to-treat analyses). Thus, even if treatment is initiated early in asymptomatic patients with preserved CD4 counts, three drugs are necessary to achieve sustained decreases of HIV load in blood and lymphoid tissue.

Adult↗
PubMed2000

[Effectiveness of morphine by periarticular injections after shoulder arthroscopy].

Peripheral opioid receptors have been found in inflamed synovia and the analgesic effect of intra-articularly administered morphine after arthroscopic knee surgery has been proven. There is controversy about efficacy of intraarticular morphine after shoulder arthroscopy. Thirty-two patients with impingement syndrome underwent subacromial decompression in the course of arthroscopic shoulder surgery. At the end of the operation morphine (5 mg) or saline was injected periarticularly. Pain intensity (rest and passive mobilisation) was recorded after recovery and after 1,2,4, and 24 hours (Numeric Rating Scale); the use of rescue medication (piritramide by patient controlled analgesia) was noted. No relevant pain reduction was apparent in the morphine group. Piritramide consumption was identical in both groups (19.7 +/- 16 mg vs. 19.8 +/- 19 mg). We conclude that periarticularly administered morphine in arthroscopic subacromial decompression in the dosage applied in this study does exert no relevant analgesic effect. This is possibly due to the fact that either subacromial tissue, despite of chronic inflammation, does not show the same reagibility as synovia or it is a problem of the nearly complete resection of the subacromial bursa.

Adult↗
PubMed2000

[Vulvodynia].

Vulvodynia is a complex syndrome of chronic vulvar pain. It is divided into several subtypes: 1. cyclic vulvovaginitis (pain occurs after coitus), 2. vulvar vestibulitis syndrome (pain mainly with intercourse), 3. dysaesthetic vulvodynia (psychosomatic; diagnosis of exclusion), 4. vulvar dermatoses (e.g. pemphigus vulgaris, contact dermatitis). Additional causes have been described in single cases. Though vulvodynia is often accompanied by psychological distress, somatic causes have to be considered in each case.

Adolescent↗