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Biomedical subjects

F W Schneider

Publications and source records attributed to F W Schneider.

At least 19 recordsLinked to original sources
PubMed2002

Laser scanning microscopy study on adsorption of biologically relevant proteins on implant materials.

The adsorption of proteins at implant surfaces plays a key role in osseointegration and is therefore of great importance in biomaterial science. Laser scanning microscopy (LSM) is described, a method that is used here for the first study of the adsorption of proteins on implant surfaces. These LSM measurements provide information on the surface morphology, and the spatial distribution of adsorbed proteins can be deduced.

Adsorption↗
PubMed2001

Control and coupling of spiral waves in excitable media.

We report the complex dynamics of spiral waves observed in the ferroin-catalyzed BZ reaction. The reaction is run in an open unstirred reactor (CFUR) with the catalyst immobilized on a polysulfone membrane. The catalyst-loaded membrane is placed between two well stirred compartments which are fed with solutions of sulfuric acid/malonic acid/bromide and sulfuric acid/bromate, respectively. An electrical field perpendicular to the membrane can be applied via Pt-ring electrodes or, alternatively, via transparent electrodes made of ITO-coated glass. In the field-free case relatively simple target and spiral patterns are observed in the membrane. If an alternating electrical field is applied the spiral core drifts through the membrane. The actual trajectory of the spiral tip depends on the amplitude and frequency of the applied electrical field. If the perturbation parameters are chosen properly the wave fronts break up and new spiral cores emerge under the influence of the alternating field. Complex spatio-temporal patterns may be induced which are reminiscent of "spiral-chaos". After switching off the perturbation the system returns to its previous, "simple" behaviour. Our experimental observations are confirmed by model calculations based on the Barkley model of spiral waves. The technique of using modulated excitability to control the dynamics of spiral waves is further extended to the coupling of two spirals in two CFURs. We present numerical simulations based on two identical excitable reaction-diffusion (RD) systems which are mutually coupled. The coupling is based on the observation of an arbitrarily chosen point inside each of the RD systems: If a chemical wave passes the point of optical observation in system 1 an electric field is applied to system 2 and vice versa. Thus, a local observation made in one system is transformed in a global perturbation of the second CFUR. We report the observation of CFUR states where the two spiral waves are spatially and temporally coupled to each other.

Journal Article↗
PubMed2000

Calcium-induced conformational change in fragment 1-86 of factor X.

Time-resolved fluorescence of the single tryptophan residue Trp41 in fragment 1-86 of factor X (FX F1-86) is studied using a time-correlated single photon counting technique with synchrotron radiation as the excitation source. Calcium ions are believed to induce a conformational change in the N-termini of the activated factor X and other vitamin K dependent proteins, which is accompanied by a decrease in fluorescence intensity. The titration with calcium yields a sigmoidal fluorescence titration curve with a transition midpoint concentration of 0.44 mM. The wavelength-dependent tryptophan fluorescence decays of the apo-FX F1-86 (in the absence of calcium) and Ca-FX F1-86 are characterized by conventional multiexponential analysis and fluorescence lifetime distribution analysis. In the absence of calcium there are three significant classes of fluorescence lifetimes (ns) that are nearly wavelength independent: 0.55 +/- 0.08 (component A), 2.6 +/- 0.1 (component B), and 5.3 +/- 0.3 (component C). However, their preexponential amplitudes vary with wavelength. The decay associated emission spectra of the individual components show that components B and C contribute over 85% to the total fluorescence for all examined wavelengths. However, in the presence of calcium, the analysis of the time-resolved fluorescence data of Ca-FX F1-86 yields four wavelength-independent lifetimes (ns) of 0.30 +/- 0.09 (component D), 0.65 +/- 0.10 (component A), 2.7 +/- 0.2 (component B), and 5.4 +/- 0.3 (component C). Calcium addition to the apo-FX F1-86 leads to a decrease in the fluorescence intensities of components B and C while their decay times remain unaffected. In Ca-FX F1-86 an additional component D arises that has a decay time of 0.30 ns and that contributes up to 35% to the total fluorescence intensity. A comparison with a previous investigation of prothrombin fragment 1 demonstrates the extensive structural and functional homology between the N termini of prothrombin and factor X(a).

Animals↗
PubMed1998

Binding of prothrombin and its fragment 1 to phospholipid membranes studied by the solvent relaxation technique.

The phospholipid headgroup mobility of small unilamellar vesicles composed of different mixtures of phosphatidyl-L-serine (PS) and phosphatidylcholine is characterized by the solvent relaxation behavior of the polarity sensitive dyes 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and 6-palmitoyl-2-[trimethylammoniumethyl]-methylamino]naphthalene chloride (Patman). If the PS content exceeds 10%, the addition of calcium leads to a substantial deceleration of the solvent relaxation of both dyes, indicating the formation of Ca(PS)2 complexes. Addition of prothrombin and its fragment 1 leads to a further decrease of the headgroup mobility, as explained by the binding of more than two PS-molecules by a single protein molecule. Prodan monitors the outermost region of the bilayer and it clearly distinguishes between the binding of prothrombin and its fragment 1. The deeper incalated Patman does not distinguish between both proteins. The validity of the solvent relaxation technique for the investigation of the membrane binding of peripheral proteins is demonstrated by the studies of prothrombin induced changes in the steady-state fluorescence anisotropies of 1,6-diphenyl-1,3, 5-hexatriene.

2-Naphthylamine↗
PubMed1997

Solvent relaxation behaviour of n-anthroyloxy fatty acids in PC-vesicles and paraffin oil: a time-resolved emission spectra study.

Time-resolved fluorescence measurements were performed for a set of n-anthroyloxy fatty acids (n-AS; n = 2, 3, 6, 9, 12, 16) in both solvent and vesicle systems. The Stokes' shifts and the mean relaxation times calculated from the time-resolved emission spectra (TRES) are shown to be strongly dependent on the position of the fluorophore in small unilamellar vesicles (SUV) composed of phosphatidylcholine (PC), while they are essentially independent of the fluorophore position in isotropic paraffin oil. The concept of an intramolecular relaxation process which had been suggested to explain the wavelength dependence of the emission behaviour of the n-AS dyes in viscous solvents is supported by semiempirical calculations showing that a more planar conformation is favoured in the excited compared to the ground state. However, in order to explain the results in vesicle systems, the concept of intramolecular relaxation is not sufficient. Rather, we show that intermolecular solvent relaxation processes play the dominant role for the wavelength dependent emission behaviour in polar, viscous environments.

Fatty Acids↗
PubMed1997

Photochemical and photobiological studies with acridine and phenanthridine hydroperoxides in cell-free DNA.

The acridine and phenanthridine hydroperoxides 3 and 7 were synthesized as photochemical hydroxyl radical sources for oxidative DNA damage studies. The generation of hydroxyl radicals upon UVA irradiation (lambda = 350 nm) was verified by trapping experiments with 5,5-dimethyl-1-pyrroline N-oxide and benzene. The enzymatic assays of the damage in cell-free DNA from bacteriophage PM2 caused by the acridine and phenanthridine hydroperoxides 3 and 7 under near-UVA irradiation revealed a wide range of DNA modifications. Particularly, extensive single-strand break formation and DNA base modifications sensitive to formamidopyrimidine DNA glycosylase (Fpg protein) were observed. In the photooxidation of calf thymus DNA, up to 0.69 +/- 0.03% 8-oxo-7,8-dihydroguanine was formed by the hydroperoxides 3 and 7 on irradiation, whose yield was reduced up to 40% in the presence of the hydroxyl radical scavengers mannitol and tert-butanol. The acridine and phenanthridine hydroperoxides 3 and 7 also induce DNA damage through the type I photooxidation process, for which photoinduced electron transfer from 2'-deoxyguanosine to the singlet states of 3 and 7 was estimated by the Rehm-Weller equation to possess a negative Gibb's free energy of ca -5 kcal/ mol. Control experiments with the sensitizers acridine 1 and the acridine alcohol 4 in calf thymus and PM2 DNA confirmed the photosensitizing propensity of the UVA-absorbing chromophores. The present study emphasizes that for the development of selective and efficient photochemical hydroxyl radical sources, chromophores with low photosensitizing ability must be chosen to avoid type I and type II photooxidation processes.

Cell-Free System↗
PubMed1997

Photochemical and photobiological studies of a furonaphthopyranone as a benzo-spaced psoralen analog in cell-free and cellular DNA.

Photobiological activities of the benzo-spaced psoralen analog furonaphthopyranone 3 have been investigated in cell-free and cellular DNA. The molecular geometry parameters of 3 suggest that it should not form interstrand crosslinks with DNA. With cell-free DNA no evidence for crosslinking but also not for monoadduct formation was obtained; rather, the unnatural furocoumarin 3 induces oxidative DNA modifications under near-UVA irradiation. The enzymatic assay of the photosensitized damage in cell-free PM2 DNA revealed the significant formation of lesions sensitive to formamidopyrimidine DNA glycosylase (Fpg protein). In the photooxidation of calf thymus DNA by the furonaphthopyranone 3, 0.29 +/- 0.02% 8-oxo-7,8-dihydroguanine (8-oxoGua) was observed. With 2'-deoxyguanosine (dGuo), the guanidine-releasing photooxidation products oxazolone and oxoimidazolidine were formed predominately, while 8-oxodGuo and 4-HO-8-oxodGuo were obtained in minor amounts. The lack of a significant D2O effect in the photooxidation of DNA and dGuo reveals that singlet oxygen (type II process) plays a minor role; control experiments with tert-butanol and mannitol confirm the absence of hydroxyl radicals as oxidizing species. The furonaphthopyranone 3 (Ered = -1.93 +/- 0.03V) should act in its singlet-excited state as electron acceptor for the photooxidation of dGuo (delta GET ca -6 kcal/mol), which corroborates photoinduced electron transfer (type I) as a major DNA-oxidizing mechanism. A comet assay in Chinese hamster ovary (CHO) AS52 cells demonstrated that the psoralen analog 3 damages cellular DNA upon near-UVA irradiation; however, no photosensitized mutagenicity was observed in CHO AS52 cell cultures.

Animals↗
PubMed1996

Binding and relaxation behaviour of prodan and patman in phospholipid vesicles: a fluorescence and 1H NMR study.

The relative location, binding behaviour and the solvent relaxation behaviour of the polarity sensitive membrane probes 6-propionyl-2-(dimethylamino)naphthalene and 6-palmitoyl-2-[[trimethylammoniumethyl]methylamino]naphthalene chloride in vesicles composed of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine or egg yolk lecithin have been compared using steady-state and time-resolved fluorescence as well as high resolution NMR measurements. The reconstructed time-resolved emission spectra show unambiguously that the observed spectral shifts in vesicle systems have to be assigned to time-dependent solvent relaxation processes rather than to a probe relocation mechanism. All fluorescence as well as the NMR relaxation data suggest a deeper localization of Patman in the membrane, sensing a less polar and/or more restricted probe environment.

2-Naphthylamine↗
PubMed1996

Stochastic Resonance and time advance coding in chemical reactions.

Stochastic Resonance (SR) is a phenomenon which may be found in nonlinear systems close to an excitation threshold. SR is a means for enhancing a weak periodic subthreshold signal from its noisy background by adding stochastic fluctuations, i.e. in biological and physical systems. It has been proposed that SR is important for the ability of neural systems to detect weak periodic signals. In the present work we show experimentally that SR occurs in two nonlinear chemical reactions, namely in the enzymatic Peroxidase-Oxidase (PO) reaction and in the Belousov-Zhabotinskii (BZ) reaction. A small sinusoidal signal with increasing noise is imposed on the focal steady state near a subcritical Hopf bifurcation. When the threshold is crossed beyond a certain noise amplitude, the system responds with spikes. The resulting interspike histogram and the plot of the signal to noise ratio, which is evaluated from the respective Fourier spectra, pass through a maximum at an optimal external noise level. An alternative way to cross the excitation threshold without noise is the variation of the bias value of the sinusoidal signal. The variation of the bias value causes the spikes to appear earlier if the sinusoidal function is moved closer towards the threshold. This so-called time advance coding is shown experimentally for the first time in the BZ reaction by imposing sinusoidal flow rate variations using different bias values. The phenomenon has been proposed by Hopfield to be a means for analog pattern recognition.

Artifacts↗
PubMed1996

Chaos control by electric current in an enzymatic reaction.

We apply the continuous delayed feedback method of Pyragas to control chaos in the enzymatic Peroxidase-Oxidase (PO) reaction, using the electric current as the control parameter. At each data point in the time series, a time delayed feedback function applies a small amplitude perturbation to inert platinum electrodes, which causes redox processes on the surface of the electrodes. These perturbations are calculated as the difference between the previous (time delayed) signal and the actual signal. Unstable periodic P1, 1(1), and 1(2) orbits (UPOs) were stabilized in the CSTR (continuous stirred tank reactor) experiments. The stabilization is demonstrated by at least three conditions: A minimum in the experimental dispersion function, the equality of the delay time with the period of the stabilized attractor and the embedment of the stabilized periodic attractor in the chaotic attractor.

Algorithms↗
PubMed1994

Influence of vesicle curvature on fluorescence relaxation kinetics of fluorophores.

The effect of membrane curvature on the fluorescence decay of 2-p-toluidinyl-naphthalene-6-sulfonic acid (TNS), 2-(9-anthroyloxy) stearic acid (2-AS) and 12-(9-anthroyloxy)-stearic acid (12-AS) was investigated for egg lecithin vesicles of average diameter dm = 22 nm and 250 nm. The biexponential fluorescence decay of TNS at the red edge of the emission spectrum was analysed according to the model of Gonzalo and Montoro [1]. Over the entire temperature range (1-40 degrees C) the small TNS labelled vesicles showed significantly shorter solvent relaxation times tau(r) than their larger counterparts (e.g. 1.3 ns compared with 2.1 ns at 5 degrees C), indicating a higher mobility of the hydrated headgroups in the highly curved, small vesicles. The fluorescence decay of both AS derivatives is also biexponential. While the shorter decay times (1-3 ns) are practically identical for small and large vesicles, the longer decay times (5-14 ns) are identical only for 12-AS but not for 2-AS. This indicates that the microenvironment is similar in small and large vesicles deep in the membrane in spite of the differences in curvature.

Journal Article↗
PubMed1987

Computer simulation of T3/T7 phage infection using lag times.

A minimal mechanism is proposed which describes the transcriptional and translational processes for four phage proteins (RNA polymerase, DNase, primase and DNA polymerase) involved in T3/T7 DNA replication. Phage DNA replication is also included. It is shown how lag times may be incorporated into a kinetic mechanism. The distinct three-stage transport of phage DNA into the bacterial host (E. coli) is considered. DNA transport is assumed to be rate-determining for the transcription of class I and II proteins. Transcriptional and translational lag times have been calculated on the basis of available gene mapping of T7 phages. The kinetic behavior of T7 and T3 phage infection is practically identical. The hydrolysis of bacterial DNA by phage DNase (endonculease and exonuclease) as well as the subsequent phosphorylation to the deoxymononucleoside triphosphates are assumed to be rate-determining in phage DNA replication. Good agreement with experiment is obtained in our computer simulations.

Computer Simulation↗
PubMed1982

Induced hydrolytic activity of yeast phenylalanyl-tRNA synthetase by tRNAPhe-CC.

"Induced hydrolysis" a new hydrolytic activity, was found by measuring AMP-production during aminoacylation of tRNAPhe-CCA by yeast phenylalanyl-tRNA synthetase in the presence of tRNAPhe-CC under conditions of low ionic strength at pH 8.5. Experiments using the elongation factor Tu . GTP provide evidence that transfer of phenylalanine to the tRNAPhe-CCA is followed by rapid hydrolysis in the presence of tRNAPhe-CC. A simple mechanism shows good agreement with the experimental data.

Amino Acyl-tRNA Synthetases↗
PubMed1982

Fluorescence of intramolecular and intermolecular interactions of aminonaphthyl-sulfonate with nucleotides.

Fluorescence studies of the intramolecular and intermolecular interactions between aminonaphthylsulfonate and nucleotides of uracil or adenine are described. The fluorescence originates solely from the naphthyl moiety and is intramolecularly quenched by the base, uracil being more effective than adenine. The enzymatic splitting of the molecule into a nucleoside monophosphate and the pyrophosphate product of the aminonaphthylsulfonate removes the intramolecular quenching and, especially in the case of uracil, a drastic increase of the fluorescence intensity results. The intact molecule exists predominantly in the folded form except in cases where electrostatic repulsion exceeds the stacking attraction. This is borne out by the pH dependence and the existence of a pronounced solvent-isotope effect of the fluorescence quantum yield for the uracil derivative at basic pH. At pH values above the pK of the enol proton of the uracil base the fluorescent properties of the intact and phosphodiesterase-digested molecules are very similar. The intermolecular interactions between 1-aminonaphthalene-5-sulfonate with AMP and UMP can be explained on the basis of dynamic quenching (collisional quenching) without any significant participation of ground-state complexes (static quenching). The interaction of the pyrophosphate adduct of 1-aminonaphthalene-5-sulfonate with UMP can best be explained by invoking two interacting nucleotide species: the free nucleotide and a sodium-nucleotide complex.

Adenine Nucleotides↗
PubMed1972

3':5'-cyclic adenosine monophosphate phosphodiesterase: negative cooperativity.

Kinetic and chromatographic analysis of cyclic nucleotide phosphodiesterase (EC 3.1.4.c) obtained from rat tissue has revealed that this enzyme exists in at least two molecular forms. After chromatographic separation, one form (cyclic AMP phosphodiesterase) still exhibits kinetics suggestive of the action of either two enzymes or one enzyme under negative cooperative regulation. Computer model studies were undertaken to distinguish between these two possibilities. The matrix method was used to generate the partition functions for (a) the sum of two independent enzymes and (b) one enzyme exhibiting negative cooperative kinetics. The experimental data were fitted to the theoretical models by a nonlinear least-squares computer program. The results show that, while both models can fit the data, the two-enzyme model would require contamination far in excess of what is detectable physically or by activity measurements. Thus, the negative cooperative model seems the more appropriate theoretical explanation of the observed kinetic behavior of this enzyme. The implication of negative cooperativity with respect to the regulation of cyclic AMP concentrations in physiological systems is discussed.

Adipose Tissue↗