Showing papers by "University of Bremen published in 1984"

Inhibitory action of certain cyclophosphate derivatives of cAMP on cAMP-dependent protein kinases

Abstract: A series CAMP derivatives with modifications in the adenine, ribose and cyclophosphate moiety were screened for their binding affinity for ;the two types of CAMP-binding sites in mammalian protein kinase type I. In addition, the activation of the kinase by these analogs was monitored. The binding data indicate that CAMP is bound to both sites in a comparable manner : the adenine appears to have no hydrogen-bond interactions with the binding sites, whereas the ribose may be bound by three hydrogen bonds involving the 2’, 3’ and 5’ positions of CAMP. The binding data are not conclusive about the nature of the interaction with the exocyclic oxygen atoms on phosphorus, though a charge interaction seems to be absent. The cAMP molecule seems to be bound in the syn conformation. The results of activation experiments show that modifications in the adenine and ribose moiety do not affect the maximal activation level, while alteration of the two exocyclic oxygen atoms may result in a reduced maximal activation level and in one case, (RJ-adenosine 3’, 5’-monophosphorothioate [R,-CAMPS], in total absence of activation even at concentrations at which the analog saturates both binding sites. Since occupancy of the CAMPbinding sites by this derivative apparently did not lead to activation of the enzyme, we examined whether this compound could antagonize: the activation by CAMP. Indeed (RJ-CAMPS was found to inhibit CAMP stimulated kinase activity at concentrations compatible to its binding affinity. Also with mammalian protein kinase type I1 (R,)-CAMPS showed antagonistic activity, while with a CAMP-dependent protein kinase from Dictyostelium discoideum partial agonistic activity was observed. Previously a mechanism for activation of protein kinase type I was proposed involving a charge interaction between the equatorial exocyclic oxygen atom and the binding site [De Wit et al. (1982) Eur. J. Biochem. 122, 95 - 991. This was based on measurements with impure preparations of (R,)-CAMPS and the R, and S, isomers adenosine 3’, 5’-monophosphodimethylamidate, cAMPN(CH,), . The present work using highly purified compounds suggests the absence of a charge interaction, since the uncharged analog (S,)-cAMPN(CH,), activates the kinase effectively. The data seem compatible with an activation model involving the formation of a covalent bond with phosphorus in both CAMP binding sites. It is well established that mammalian CAMP-dependent protein kinases are activated by a CAMP-induced release of free (active) catalytic subunits from a tetrameric holoenzyme [l]. The holoenzyme consists of two catalytic and two regulatory subunits and each regulatory subunit binds two molecules of cAMP to distinct sites. In the cellular slime mold Dictyosteliurn discoideum a CAMP-dependent protein kinase has been reported which showed different properties. The holoenzyme apparently consists of more than four subunits, the 40-kDa regulatory subunit contains one type of CAMPbinding site and the catalytic subunits often form large aggregates [2 - 51. Mammalian CAMP-dependent protein kinases have been studied using over 200 derivatives of CAMP. Recently several derivatives were observed to bind with clearly distinct affinity to the two types of binding sites, suggesting a difference in structure of the binding sites [6 -91. The use of these selective analogs led to the conclusion that both sites are involved in the activation of the kinase [I0 - 121.

ANNA: a language for annotating Ada programs

Abstract: ANNA is a proposed language extension of Ada to include facilities for formally specifying the intended behavior of Ada programs (or portions thereof) at all stages of program development. Anna programs are Ada programs extended by formal comments. Formal comments in ANNA consist of virtual Ada text and annotations. Anna provides annotations for all Ada constructs, including declarative annotations (for variables, subtypes, subprograms, and packages), statement annotations, annotations of generic units, exception annotations and visibility annotations. (The current Anna design does not include extensions for annotating Ada multi-tasking constructs.) Anna also includes a small number of new predefined attributes, which may appear only in annotations, e.g. the collection attribute of an access type. Since all Anna extensions appear as Ada comments, Anna programs are also legal Ada programs and acceptable by Ada translators. The semantics of annotations are defined in terms of Ada concepts; in particular, many kinds of annotations are generalizations of the Ada constraint concept. This simplifies the training of Ada programmers to use Anna for formal specification of Ada programs. Anna provides a formal framework within which different theories of formal specification may be applied to Ada. This manual also describes a translation of annotations into Ada text for run-time check of consistency with annotations.

Task-specific EMG-characteristics during mental training.

Abstract: Despite a sixty-year tradition of research into “ideomotor reaction” it is not yet clear, whether myoelectric activity measured during mental training contains only inner-organismic or in addition task-specific information. Our investigation involved one group trained actively in a sensorimotor task (paced contour-tracking), another group which was intermediately instructed to train on a mental level, and a third (control) group which had no instruction for training in the intermediate performances. Measurements were taken of the muscular activity (EMG) of the main working muscle (m. biceps) synchronously to the motion of the target in all three groups. The data were submitted to several time series analysis procedures: auto-correlative measures and power spectra. Correlations were found between the filtered time series of the track and the EMG-activity in the mental training performances. The frequency distribution in the power spectra of the track was found in the power spectra of the active as well as in the mental training groups but not in those of the controls. The results indicate that the myoactivity during mental training clearly shows a task-specific frequency distribution.

A stopped Doob inequality for stochastic convolution integrals and stochastic evolution equations

Abstract: A stopped Doob inequality is proved for stochastic convolution integrals in Hilbert space, where M is a square integrable Hilbert space valued cadlag martingale, ⊘ an operator valued predictable function and U(t, s) a contraction-type evolution operator. This allows to obtain the mild solution for evolution equations (with memory) where A(t) is the quasigenerator of U(t,s), V(t) a bounded variation process, and Z(t) a semimartingale, under the same weak assumptions on B and D as for stochastic differential equations with bounded coefficients, i .e ., (A( t) = 0) . Moreover, a weak convergence criterion for is derived.

The dynamics of recurrent inhibition.

Abstract: A heuristic model for the dynamics of recurrent inhibition, emphasizing non-linearities arising from the stoichiometry of transmitter-receptor interactions and time delays due to finite feedback pathway transmission times, is developed and analyzed. It is demonstrated that variation in model parameters may lead to the existence of multiple steady states, and the local stability of these are analyzed as well as the occurrence of switching behaviour between them. As an example of the applicability of this model, parameters are estimated for the hippocampal mossy fibre-CA3 pyramidal cell-basket cell complex. Numerically simulated responses of this system to alterations in presynaptic drive and titration of inhibitory transmitter receptors by penicillin are presented. Numerical simulations indicate the existence of multiple bifurcations between periodic solutions, as well as the existence of bifurcations to chaotic solutions, as presynaptic drive and receptor density are varied. It is hypothesized that the model offers insight into the sequences of events recorded in single CA3 pyramidal cells following the application of penicillin, a specific inhibitory receptor blocking agent.

pH-preferences and habitat selection in carabid beetles.

Abstract: Seven species of carabid beetles were examined in different "pH-Orgeln" for pH-preferences. Five of these species showed significant preferences for specific pH-fields. Presumably, this parameter of distribution found in the laboratory is also effective in the field. We caught the beetles in the field on soil of the same pH-values which they prefered in the laboratory. The pH-measurements taken by previous workers in the field match our results.The receptors for H-ions are probably located on the antennae, because the preference distribution of Pt. angustatus changed into a uniform distribution after amputation of the distal segments of the antennae. The structure of these receptors could not be identified in electron microscope pictures (REM) among the multitude of different receptors on the antennae.

Decentralized control of dynamically interconnected systems

Abstract: Interconnected systems, where the subsystems are interconnected by some dynamic interaction system, are considered. It is shown that this type of system can be stabilized by decentralized dynamic output feedback, if the subsystems are stabilizable by (centralized) dynamic output feedback and the interaction system is stable. The relation to previous results is discussed.

Investigations on stimulation of lac transcription in vivo in Escherichia coli by cAMP analogues. Biological activities and structure-activity correlations.

Abstract: The ability of 24 systematically modified analogues of adenosine 3′,5′-monophosphate (cAMP) to enhance the synthesis of β-galactosidase in glucose-repressed Escherichia coli strains KNBL 1001 and cpd– Crookes has been investigated. The properties of the analogues in comparison with cAMP are, with only two exceptions, alike in both strains. Two analogues, 7-deazaadenosine 3′,5′-monophosphate (i.e. tubercidin 3′,5′-monophosphate) and (Rp)-adenosine 3′,5′-monothionophosphate, exhibit higher biological activity than cAMP. The latter analogue is 50-fold more active in both strains. Three analogues showed activities comparable to cAMP, four analogues were less active and 12 analogues were unable to antagonize catabolite repression. Structure-activity correlations showed that the 2′OH-, 3′O-, 5′O-, the negative charge and the 6-amino group cannot be modified without losing biological activity in vivo, while the N-1 and N-7 in adenine are not essential. The interaction with the catabolite gene activator protein is stereoselective for an unmodified axial exocyclic oxygen. The results are compared to those obtained with cAMP analogues in E. coli in vitro and those obtained with the same analogues in protein-kinase systems and Dictyostelium species. The model of McKay et al. [McKay, D. B., Weber, J. T. and Steitz, T. A. (1982) J. Biol. Chem. 257, 9518–9524] proposed for distinct chemical interactions of cAMP with the catabolite gene activator protein is discussed and supplemented by additional hydrogen bond interactions.

Re‐evaluation of decision alternatives dependent upon the reversibility of a decision and the passage of time

Abstract: In the present experiment subjects made a decision between two alternatives which was either reversible or irreversible After the choice, subjects evaluated the attractiveness of both alternatives once more under different time levels It was found that with increasing time level, re-evaluation of alternatives increased under irreversible and decreased under reversible conditions The results are discussed in the framework of dissonance theory

Chaos in Classical Mechanics: The Double Pendulum

Abstract: The dynamics of a double pendulum is presented in terms of Poincare sections. It is shown that the simple classical textbook example displays all the complexity of non-integrable Hamiltonian systems.

Broadband dual-depth E-plane corrugated square waveguide polariser

Abstract: The computer-aided design of a dual-depth E-plane corrugated waveguide polariser is described which achieves 90±1° differential phase shift between the TE10− and TE01− wave transmission coefficient for 11.2–14.8 GHz. The method of field expansion into suitable eigenmodes used considers the effect of higher-order-mode interaction at the step discontinuities.

Investigation of intracellular phosphate pools of the green alga Chlorella using 31P nuclear magnetic resonance

Abstract: 31P NMR measurements were performed in order to study the intracellular phosphate pools of the green alga Chlorella fusca. Cells of asynchronous cultures contain a large pool of polyphosphates, whereas the amount of polyphosphates in cells of synchronous cultures depends on the state of differentiation. The assignment of extracellular and intracellular inorganic orthophosphate is achieved by changing the pH, whereas the intracellular compartmentation of inorganic orthophosphates and sugar phosphates is shown during irradiation of the cells with light within the NMR spectrometer.

Model reactions of chromium compounds with mammalian and bacterial cells

Abstract: Chromate uptake, reduction, cytotoxicity and mutagenicity were studied with human red blood cells, Chinese hamster ovary (CHO) cells and/or Salmonella typhimurium mutant cells. All cell types rapidly took up chromates whereas chromium(III) salts were excluded under the experimental conditions. Red blood cells reduced and accumulated chromium from chromate. At concentrations above 0.1 mM, chromate inactivated the red cell chromate carrier. Chromate above 0.01 mM inhibited CHO cell proliferation irrespective of the cations present. Chromate and two chromium(III) complexes were mutagenic with Salmonella mutants in the Ames’ assay. A model for chromate metabolism and genotoxicity is proposed.

Polymeric schiff's base chelates and their precursors, 7. Dioxygen binding and catalytic oxidation of 2,6-di-tert-butylphenol†

Abstract: Dioxygen binding and catalytic oxidation of 2,6-di-tert-butylphenol(9) were investigated by employing various low molecular chelates (1 and 2), covalently or coordinatively bound polymeric chelates (3, 4, 5, 6, and 7), and polymeric Schiff's base chelates (8). Particularly the covalently bound polymeric chelates 3 and 4 were found to exhibit activities similar to low molecular 1 in regard to dioxygen binding. It is suggested that these polymers can reversibly form mononuclear superoxo-complexes. In the oxidation of 9 the covalently bound polymeric chelates 3 – 5 exhibit good activity which does not decrease after repeated use.

Concepts of Reduction and Dispersion of Metals in Zeolites

Abstract: Experimental observations concerning the formation, dispersion and stability of metal phases in stoichiometrically ion-exchanged zeolites are reconsidered on the basis of (i) redox equilibria, taking into account ion activities and zeolite lattice rearrangements, and (ii) possible nucleation mechanisms of metal clusters. New experimental evidence for the existence of an orientation relationship between platinum crystals and the surrounding zeolite matrix is presented and discussed.

Correlation of Simultaneously Measured Droplet Sizes and Velocities in nozzle sprays

Abstract: The application of a new LDA method which simultaneously measures the size and velocity of small water droplets in the spray cone of a fan type water nozzle is described. As the phase difference between adjacent photomultipliers responding to signals from a fringe mode LDA is linearly proportional to the diameter of the spherical particle in the measuring volume, the new instrument allows, for long distances between the optical devices and the measuring volume in the spray, non-invasive measurements and from these the correlation of size and velocity of the individual droplet in order to establish two-dimensional distributions. From the new LDA instrument one receives definite information about the volume-flow concentration in the measuring point of an enclosed flow situation.

Kinetically Controlled Semisynthesis of β‐Lactam Antibiotics and Peptidesa

Abstract: where an activated substrate must be used, and the enzyme carries out a group transfer reaction. The yield of the desired product in this case is often much larger than the yield for the equilibrium-controlled process.'-' This requires that the catalyst be removed when the maximum is reached, and this is easily performed with immobilized enzymes. The detailed reaction mechanism for the kinetically controlled process' must be known for' a rational analysis of the factors controlling yield. Two different mechanisms have been proposed here. They are given in TABLE I . The mechanism without binding of the nucleophile N (6-APA i n Eq. 2, or an amino-acid derivative in peptide semisynthesis), before the deacylation of the acylenzyme E-A, is the most frequently used mechanism in the literature in this field. The other mechanism where the nucleophile N is bound to the acylenzyme before the deacylation may be inferred from the sequence specificity of the hydrolases and the principle of microscopic reversibility. The two mechanisms can be distinguished by measuring the initial rates of formation of AN (oaN) and A (uA) as functions of nucleophile concentration. The expressions for this and the yield at the kinetically controlled maximum are given in TABLE I.' Once the mechanism has been established, the yield-controlling factors can be rationally analyzed to evaluate the biotechnological potential of such processes. Some data pertinent to the kinetically controlled, enzyme-catalyzed synthesis of semisynthetic penicillins and peptides are presented here. Free and immobilized penicillin amidase (EC 3.5.1.1 1) from E. coli, the substrates and 6-APA used to prepare semisynthetic penicillins were gifts from Dr. Sauber (Hoechst AG) and Dr. Kramer (Rohm), respectively. Phenyl-acetyl-glycine was