bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluorescence Emission Properties of the Cation of 4-Aminopyrazole(3,4-d) pyrimidine, an Adenine Analogue: Evidence for Phototautomerism
Authors: Wierzchowski Jacek , Szczęśniak Marian , Shugar David 
Published: August 2018

A study has been made of the emission spectra at room temperature, in aqueous and alcoholic media, of 4-aminopyrazolo(3,4-d)pyrimidine (APP) and some of its methylated derivatives. The cationic forms APPH+, N2-methyl-APPH+ and N7-methyl-APPH+ exhibit intense fluorescence un­der these conditions, the first two exhibiting excitation spectra which differ from the absorption spectra, pointing to the existence of a tautomeric equilibrium in the ground state. From the shape of the excitation spectra, and comparisons with methylated analogues in fixed tautomeric forms, it follows that the emission of APPH+ originates exclusively from the species N(2)-H,N(7)-H+, the other forms being non-fluorescent. The proportion of the emitting species, calculated from the ex­citation wavelength dependence of the quantum yield, is in good agreement with data for the ground state.
The emission spectrum of APPH+ in aqueous medium consists of two bands with λmax 360 nm and 430 nm, which exhibit identical excitation spectra, but are quenched to different extents by H3O+. The 430 nm emission band is absent in alcoholic media. A similar behaviour is exhibited by N7-methyl-APPH+, whereas the neutral form of this analogue exhibits only the 430 nm band. These results indicate that the long wavelength emission band of APPH+ originates from the rare tautomeric species N(7)-H formed in the excited state by photodissociation of the N(2)-H proton from the species N(2)-H,N(7)-H+. This is further confirmed by results obtained with the aid of the basicity method, as well as by salt efects in non-aqueous media. Consideration is given to the possibility of such processes occurring in other analogues of nucleic acid derivatives.
Small-Angle X-Ray Scattering Studies on the X-Ray Induced Aggregation of Malate Synthase Computer Simulations and Models
Authors: Zipper Peter , Durchschlag Helmut 
Published: August 2018

Malate synthase undergoes an X-ray induced aggregation which can be monitored in situ by small-angle X-ray scattering; the analysis of scattering curves, taken at subsequent stages of aggregation, has led to the establishment of a tentative model for an aggregation in two dimensions (Zipper and Durchschlag (1980) Rad. and Environm. Biophys., in press).
This model was checked by comparison of appropriate theoretical curves with the experi­mental curves. The theoretical scattering curves for this comparison were obtained by weighted averaging over the scattering curves calculated for various species of hypothetical aggregates. Based on the approximation of the unaggregated enzyme particle by an oblate cylinder, the aggregates were assumed to be composed of 2, 3, 4 or 6 of such cylinders, associated side-by-side in one and later on in two linear rows. The weight fractions of the species were chosen so, that an optimum fit of the experimental mean radii of gyration and mean degrees of aggregation was achieved. The distance distribution functions calculated for the model are very similar to the functions derived from the scattering experiment. Cross-section Guinier plots of the scattering curves of the model reveal the occurrence of one and later on of two pseudo cross-section factors similar to those observed in the experimental scattering curves. The pseudo thickness factor of the model of the unaggregated particle is found to be retained in the model curves for all stages of aggregation. From these results it can be concluded that the model for the aggregation process is essentially consistent with the scattering behaviour of the aggregating enzyme. Small differences between the theoretical and experimental curves may be explained by the idealizations of the model. The comparison of theoretical curves for alternative models, assuming aggregation in three dimen­sions, suggests that these models are unlikely, though small amounts of three-dimensional aggregates cannot be ruled out completely.
Highly Efficient Purification of the Labile Plant Enzyme 5-Aminolevulinate Dehydratase (EC 4.2.1.24) by Means of Monoclonal Antibodies
Authors: Liedgens Walter , Grützmann Rudi , Schneider Hansjörg A. W. 
Published: August 2018

Abstract
5-Aminolevulinate dehydratase (ALAD) from spinach (Spinatia oleracea) was isolated by affinity purification on an immunoabsorbens with a yield of 70 to 80% of the activity in the crude enzyme preparation. The enzyme eluted from the immunoabsorbens was pure as judged by poly­ acrylamide gel electrophoresis and is a hexamer with a subunit molecular weight of about 50000. Enzyme bound to the immunoabsorbens was able to synthesize porphobilinogen in a continuous manner. Owing to the lability of the enzyme and its low abundance in plant tissue, we have been unable to obtain similar yields of purified enzyme using classical purification procedures.
This highly efficient purification was made possible by using monoclonal antibodies as described by Köhler and Milstein (Nature 256, 495 (1975)). The availability of monoclonal antibodies meant that it was not necessary to purify the enzyme to homogeneity by classical means in order to raise an antiserum specific for ALAD. Sixteen clones of cells producing anti­ bodies against ALAD were selected. They all expressed a ϰ light chain but differed in the heavy chain class which was either γ1 or γ2a.
The availability of pure ALAD enzyme and of highly specific antibodies against the enzyme now enables us to answer questions concerning properties, localization, intercellular transport and evolution of ALAD. It is clear that the technique used and the questions asked are not restricted to ALAD.
Partial Purification and Some Properties of a Hydroxycinnamoyl Glucosyltransferase from Tomato Fruits
Authors: Fleuriet A. , Macheix J. J. , Suen R. , Ibrahim R. K. 
Published: August 2018

A glucosyltransferase was isolated from immature “cherry” tomatoes and was partially purified (200-fold) by ammonium sulphate precipitation and successive chromatography on Sephadex G-100 and DEAE-cellulose columns.
The enzyme utilised the free hydroxycinnamic acids and UDP-glucose in the formation of their respective glucosides (pH 8.0) and glucose esters (pH 7.0); but did not accept the CoA thiolesters of HCAs in the presence of glucose-1-phosphate. The constant glucoside/glucose ester ratio observed during purification suggests that both reactions are catalysed by the same enzyme.
The Km values for ρ-coumaric, caffeic, ferulic and sinapic acids were 0.8, 1.5, 1.4 and 2.5 μᴍ, respectively. With ferulic acid as substrate, the Km value for UDPG was 10 μᴍ. The enzyme required an -SH group for activity and the reaction was strongly inhibited by EDTA, divalent metal ions and UDP.
"Flavanone Synthase" in Oat Primary Leaves Time Course and Distribution at the Tissue and Subcellular Level
Authors: Fuisting Klaus , Weissenböck Gottfried 
Published: August 2018

Abstract
“Flavanone Synthase” (FS) isolated from oat primary leaves shows maximal activity in the differentiating zone of five day old leaves. Activity of FS is distributed in both the upper and lower epidermis, but dominant in the mesophyll. After fractionation of mesophyll protoplasts of Avena by differential centrifugation, FS activity could only be detected in the “cytosol” and not in intact chloroplasts or other particulate fractions.
A Convenient Method for the Preparation of Pheromones from Inexpensive Starting Materials
Authors: El-Rabbat Nawal A. , Mangold H. K. 
Published: August 2018

Abstract
-9-Tetradecenoic acid was isolated from the total fatty acids of beef tallow. (Z)-9-Tetradecenol, (Z)-9-tetradecenyl acetate and (Z)-9-tetradecenal, compounds known to function as sex attractants in various insect species, were prepared from this fatty acid.
Infection of Murine T Lymphocytes with Lymphocytic Choriomeningitis Virus: Effect of Age of Mice on Susceptibility
Authors: Tijerina Rolando , Löhler Jürgen , Chaturvedi Umesh C. , Lehmann-Grube Fritz 
Published: August 2018

Abstract
Infectious T lymphocytes were determined in thymuses and spleens of mice acutely infected with LCM virus. Such cells appeared in newborn animals, but their numbers declined when the age at infection increased and none were found in adult mice. Either susceptibility to LCM virus is associated with some degree of immaturity or the probability of murine T lymphocytes to encounter the virus as an infectious entity rather than an immunogen is higher in very young than in immunologically mature mice.
Ecdysteroid Titres during Autonomous Metamorphosis in a Dermestid Beetle
Authors: Delbecque Jean-Paul , Sláma Karel 
Published: August 2018

The larvae of Dermestes maculatus are able to undergo several moults in complete absence of the cephalic and prothoracic neuroendocrine system, showing thus spontaneous metamorphosis. Measurements of ecdysteroid contents by radioimmunoassay methods have revealed distinctive larval, prepupal and pupal ecdysteroid peaks, as found in other species where development requires frequent stimulation by the centrally produced hormones. Mass fragmentographic analysis has indicated that more than 80% of the ecdysteroids detected by the radioimmunoassay during the peaks consists of ecdysterone.
The prothoracic glands (PG) of D. maculatus larvae are located in the head capsule and in the cervical region. They can be separated from the body by neck-ligation. Only the larval peak of ecdysterone can be correlated with PG function. The prepupal and pupal peaks of ecdysterone are not produced by the central neuroendocrine system. The isolated abdominal fragments of larvae and pupae positively produce ecdysteroids in the course of their independent development, but this synthesis has been subnormal and occasionally delayed in time. In contrast, the isolated thoracic fragments produce well synchronized peaks of ecdysterone and this does not depend on the PG. It thus appears that some thoracic tissue other than PG is able to maintain the physiological concentration of ecdysterone by means of a concentration-dependent feed-back mechanism.
Due to spontaneous metamorphosis and extremely good survival we have succeeded to induce in this species: a) premature formation of the prepupal cycle of ecdysterone synthesis in the penultimate larval instar by ligation; b) inhibition and delay of the prepupal peak by means of juvenoid treatments; c) reappearance of the prepupal peak in the inhibited “permanent larvae” by exogenous administration of ecdysterone, or; d) modification of the pupal peak by a qualitatively new pupal-pupal one after juvenoid treatments. These experimental transformations of the ecdysterone peaks have suggested that the kind and nature of the peaks are closely related to nature and stage of the ontogenetic development. We therefore believe that the process of larval-pupal reprogramming has occurred in this species long before the increase of ecdysterone titer in the body. Both the prepupal and pupal peaks do not represent a cause but they show to be rather consequences of the developmental programming. Further features associated with possible physiological role of ecdysteroids in insect development have been briefly discussed.
Freeze-Fracture Evidence of Differences between Membranes of Perialgal and Digestive Vacuoles in Paramecium bursaria
Authors: Meier Renate , Reisser Werner , Wiessner Wolfgang , Lefort-Tran Marcelle 
Published: August 2018

Abstract
Measurements of particle densities on the two freeze-fracture faces of digestive and perialgal vacuole membranes in green and aposym biotic Paramecium bursaria Ehrbg. show distinct differences between the P-faces of both membrane types. The distribution of particle densities is more homogenous on the P-faces of perialgal vacuole membranes than on the P-faces of digestive vacuole membranes. Possibly homogeneity among peri­ algal vacuole membranes reflects the stability of perialgal vacuoles during their life cycle. Perhaps lysosomes cannot fuse with them.
Zum Farbunterscheidungsvermögen der Honigbiene bei niedrigen Umgebungshelligkeiten / Colour Discrimination of the Honey Bee at Low Light Intensities
Authors: Pflughöft Gerhard 
Published: August 2018

Abstract
Homing foragers of the honey bee (Apis mellifera carnica) were tested for discrimination of colour marks presen­ted to them at the hive entrance. At a low rate of natural il­lumination the bees were not able to distinguish the coloured (yellow, blue) marks from those with a corresponding gray. However, their general orientation was not disturbed. From this the conclusion is drawn that at low light intensities bees have an achromatic vision besides their known co­ lour vision at higher intensities.
Denaturation and Renaturation of Bovine Liver Glutamic Dehydrogenase after Dissociation in Various Denaturants
Authors: Müller Klaus , Jaenicke Rainer 
Published: August 2018

Abstract
Oligomeric glutamic dehydrogenase from bovine liver is dissociated to inactive monomers (Mr = 56 000) under a wide variety of conditions: 3 ≥ pH ≥ 12, 6 ᴍ guanidine · HCl, 6 ᴍ urea, 0.2% sodium dodecylsulfate. High hydrostatic pressure (< 1 kbar) only affects the association equilibrium of the native hexamer to higher polymers. The respective reaction volume (ΔV=28 ± 5 ml · mol-1 at 298 K, 1 bar) is linearly dependent on temperature and pressure. At p > 1.5 kbar dissociation of the hexamer occurs; this reaction is accompanied by irreversible deactivation.
Depending on the denaturant applied for the monomerization, the final conformational stale of the polypeptide chain differs widely regarding its residual structure.
As taken from laser light scattering measurements the rate of dissociation at pH 1.8 follows first order kinetics with a rate constant k1 = 0.42 ± 0.06 s-1.
In the range of the oligomer ⇌ monomer transition, dissociation is accompanied by irreversible aggregation leading to inactive high molecular weight material. At low concentration (c < 5 µg/ml) this side reaction can be slowed down, so that the reconstitution of the enzyme can be monitored using spectroscopic techniques. Concentration dependent stopped-flow experiments prove the regain of fluorescence to be a rapid first order process; the respective half-times at pH 7.4 are τ1/2 = 2.0 ± 0.5 ms and 0.7 ± 0.2 ms for the “renaturation” from 6 ᴍ guanidine · HCl, pH 6, and pH ~ 2, respectively.
The product of reconstitution shows the fluorescence and circular dichroism pattern characteristic for the native enzyme. However, no reactivation can be achieved under any of the following conditions: optimum protection against chemical modification; variation of enzyme concentration, temperature, and hydrostatic pressure; addition of specific ligands such as coenzymes, substrates, ADP, membrane constituents (cardiolipin, electron transfer particles ETPH). Obviously, the “renaturation” (D → N) of glutamic dehydrogenase is governed by a side reaction according to
N → D ⇌ R → A
which causes aggregation of intermediates R instead of reconstitution of the native enzyme.
The Activation of Ribulose-1,5-bisphosphate Carboxylase-Oxygenase from Spinach by Oxygen / Changes of the Enzyme Conformation during Air-Argon Transitions
Authors: Wildner Günter F. , Sane Prafullachandra V. , Henkel Jürgen 
Published: August 2018

Abstract
The effect of oxygen on ribulose-1,5-bisphosphate carboxylase-oxygenase from spinach was in­vestigated. Both activities were deactivated by removal of oxygen and reversibly reactivated by oxygenation of the enzyme solution. The change in enzyme activities was accompanied by conformational changes as studied by the use of intrinsic and extrinsic fluorescent probes.
The analysis of cysteine sulfhydryl groups accessible to 5,5′-dithiobis-(2-nitrobenzoic acid) revealed that the number of these groups changed with the oxygen concentration. The kinetic of the exposure of eight cysteine residues was similar to the loss of enzyme activities. The modification of these groups with 5,5′-dithiobis-(2-nitrobenzoic acid) caused almost complete loss of both the activities.
The enzyme isolated from a photolithotrophic organism, Chromatium vinosum, was not affected by oxygen removal. During air - argon transitions, neither the enzyme conformation nor the number of accessible sulfhydryl groups changed.
Cytotoxicity of Cobra (Naja naja kaouthia) Venom on Rabbit Red Blood Cells and S-180 Tumor Cells in the Presence of Tetracaine, Lidocaine and Procaine
Authors: Li Ping-Lu 
Published: August 2018

Abstract
The cytocidal action of Naja naja kaouthia venom on rabbit red blood cells and S-180 tumor cells treated with local anesthetics (tetracaine, lidocaine and procaine) were studied. The S-180 cells were more sensitive to the venom than the red blood cells which required albumin for efficient hemolysis in the 10 minute assay. All three local anesthetics at lower concentrations protected both cell types against venom hemolysis. At higher concentrations the local anesthetics enhanced the cell lysis to 100%. The effectiveness of the local anesthetics for both the inhibition and enhancement phases of cytotoxicity was tetracaine > lidocaine > procaine. This is the same order as their anesthetic effectiveness, lipid solubility and their protein binding.
Water Budget in Larvae of Semiadalia undecimnotata Schn. Studied with Tritiated Water
Authors: Buscarlet L. A. , Ferran A. , Larroque M. 
Published: August 2018

Abstract
The rates of water vapor entry, body water clearance and the net loss of water in larvae of Semi­ adalia undecimnotata (3rd and 4th stage) of different weights were determined from observed changes in the mass of body water and its tritium content for each of several relative humidities (RH) in ambient air.
The water clearance and vapor entry rates as a function of weight increases from emergence to the middle of the stage and then remains constant. The vapor entry rate increases with RH while the clearance rate is independant of RH. The permeability of the cuticle has not the same value in the inward and in the outward direction. The permeability to body water escape is not affected by RH and reaches a maximum at the middle of the stage. The inward permeability does not depend on weight and increases appreciably as RH reaches saturation.
One day of starvation affected these movements of water most in larvae at the middle of their stage.
These results are discussed in relation to some physiological data concerning the cuticular struc­ture and its evolution with age.
A Hydrodynamic Model of Cerebrospinal Fluid Flow in Man
Authors: Wüst Rolf , Kolberg Trygve , Palma Alvaro , Palma Alfredo 
Published: August 2018

Abstract
A hydrodynamic bi-compartmental model for the cerebrospinal fluid (CSF) flow in humans is presented which combines anatomical and physiological conditions in the central nervous system with results of special radioisotope diagnostic techniques. Normal and disturbed conditions, the diagnostic methods and the results are explained. A differential equation for the time behaviour of regional radioisotope concentrations is derived by applying to the model mathematical procedures which are familiar from the description of radioactive decay series, or reaction kinetics of chemical or pharmaceutical processes. The solutions are analysed and discussed with respect to findings of isotope diagnostics, and parameters for the complete and quantitative evaluation of CSF flow systems are derived. A system factor is introduced for classification purposes and, in conjunction with basic principles of hydrodynamics, is used to postulate a similarity law of CSF flow systems. The diagnostical and therapeutical value of the model for analysis and simulation of CSF flow systems is discussed. Practical applications to other disciplines are proposed.
Biochemical and Electronmicroscopic Investigations on Helix pomatia Collagen
Authors: Schmut O. , Roll P. , Reich M. E. , Palm W. 
Published: August 2018

Abstract
The skin of Helix pomatia was investigated by biochemical methods and electronmicroscope. Biochemical investigations showed that Helix pomatia collagen represents a methionine-lacking collagen resistant to CNBr-cleavage. Electron microscopic studies showed a cross striation pattern of 5 3 -5 7 nm.
Die Flavonoide der Samen von Medicago × varia Martyn c. v. Cardinal (Fabaceae) /The Seed-Flavonoids of Medicago × varia Martyn c. v. Cardinal (Fabaceae)
Authors: Gehring Eberhard , Geiger Hans 
Published: August 2018

Abstract
Medicago x varia Martyn c. v. Cardinal (Fabaceae) The Seed-Flavonoids of Medicago x varia Martyn c. v. Cardinal (Fabaceae) Medicago x varia c. v., Fabaceae, Flavonoids, 5-Methoxyflavones, 5-Methoxyflavonols From the seeds of Medicago x varia Martyn c. v. Cardinal have been isolated twenty flavonoids, including four 5-methoxyflavonoids. Four compounds have been obtained the first time from a natural source. The constitution of all compounds is prooved.
Induced Isoflavonoids of Erythrina sandwicensis
Authors: Ingham John L. 
Published: August 2018

Abstract
Two new phytoalexins isolated from the fungus-inoculated leaflets of Erythrina sandwicensis have been identified as (—)-6aS; 11 aS-3,6 a,9-trihydroxy-10-isopentenylpterocarpan (sandwicar-pin) and (—)-6aR; 11 aR-3-hydroxy-9-methoxy-10-isopentenylpterocaipan (sandwicensin). These compounds co-occur with several known pterocarpan (demethylmedicarpin, 3,6a,9-trihydroxy-pterocarpan, phaseollidin and cristacarpin) and isoflavan (demethylvestitol and isovestitol) deriva­ tives. The preparation and spectral (UV, MS) characteristics of 3-methoxy-9-hydroxy-10-isopen-tenylpterocarpan are also described.
Competition of Pyridoxal 5'-Phosphate with Ribulose 1,5-Bisphosphate and Effector Sugar Phosphates at the Reaction Centers of the Spinach Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase
Authors: Vater Joachim , Gaudszun Thomas , Schamow Harald , Salnikow Johann 
Published: August 2018

Abstract
The Stimulation of the carboxylase reaction by effectors of ribulose 1,5-bisphosphate carboxyl­ ase/oxygenase displays higher sensitivity towards pyridoxal 5'-phosphate inhibition than the catalytical process itself.
Pyridoxal 5'-phosphate binding to the enzyme is not affected by the modulators 6-phospho-gluconate and fructose 1,6-bisphosphate at low concentrations at which these agents stimulate the carboxylation rate.
At higher concentrations these sugar phosphates protect the enzyme against pyridoxal 5'-phos-phate inhibition in a similar fashion like the substrate ribulose 1,5-bisphosphate.
Such protection experiments in combination with spectrophotometrical studies of pyridoxal 5'-phosphate binding demonstrate two binding states of ribulose 1,5-bisphosphate at the reaction centers of the enzyme with different requirements for Mg2+. 6-Phosphogluconate functions as protector only in the presence of Mg2+.
Our results imply a competition between pyridoxal 5'-phosphate and substrate or effector sugar phosphates at the reaction centers of the spinach carboxylase. It is proposed that the pyridoxal 5'-phosphate inhibition of the stimulatory activity of these effectors originates from a modification of the regulatory sites of the enzyme caused by pyridoxal 5'-phosphate binding to the catalytical sites.