bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Role of Quinones in Bacterial Electron Transport
Authors: Kröger A. , Dadák V. 
Published: March 2005

The menaquinone of Bacillus megaterium (14581 ATCC) is localized exclusively in the cytoplasmic membrane as are the cytochromes. Menaquinone is contained in a 5 to 10‐fold molar excess over cytochrome b1.
The constituent menaquinone is almost completely reduced to menaquinole in the anaerobic state with the substrates respired by the membrane fraction. On the addition of oxygen the menaquinole is reoxidized to menaquinone. Menaquinone and menaquinole are the only forms of MK detected in the steady states of the electron transport.
The redox reactions of menaquinone indicate its participation in the electron transport from the substrates α‐glycerophosphate, malate and NADH, to the acceptors oxygen and fumarate. Menaquinone is in a steady state in all the flow systems established with each substrate and both acceptors, and exhibits the steady state response expected for a respiratory component.
The cytochrome system of this strain of B. megaterium consists of a b‐type cytochrome with a redox potential of + 8 mV and absorption bands close to those of pure cytochrome b1, two cytochrome oxidases, and α‐type cytochrome and cytochrome o and probably a small amount of c‐type cytochrome. Cytochrome b1 is completely reducible by each of the substrates.
2‐n‐Heptyl‐4‐hydroxyquinoline‐N‐oxide inhibits the electron flow at about the concentration of the constituent menaquinone between menaquinone and the cytochromes. The electron flow from each of the substrates to both acceptors depends completely on the reaction sensitive to the inhibitor.
The electron transport from α‐glycerophosphate, malate and NADH to oxygen and fumarate as well as the reduction of cytochrome b1 is dependent on the presence of MK. This is demonstrated by pentane extraction and reincorporation of the MK. The reincorporation leads to the reconstitution of the original pathway, since MK and cytochrome b1 participate in the electron transport and the same sensitivity to 2‐n‐heptyl‐4‐hydroxyquinoline‐N‐oxide is found.
The position of menaquinone in the respiratory system of B. megaterium is between the dehydrogenases for α‐glycerophosphate, malate and NADH and cytochrome b1 to which the fumarate reductase and the cytochrome oxidases are linked.
L'acétylcholinestérase des organes électriques de Poissons (torpille et gymnote); complexes membranaires
Authors: Massoulié J. , Rieger F. 
Published: March 2005

After extraction of the torpedo electric organ, three main molecular species, A, C, D, carrying the acetylcholinesterase activity have been found. This is observed in fresh‐frozen organ extracts, toluene‐autolysed organ extracts, or autolysis exsudate. A fourth species, B, appears during autolysis in the exsudate, or following treatment of the extracts by proteolytic enzymes, trypsin or α‐chymotrypsin. A series of agents such as pH, p‐hydroxymercuribenzoate, or pharmacological drugs, have been tried in order to modify the distribution of activity among the different species; all have failed, demonstrating the stability of these species.The two species which migrate faster in a sucrose gradient, C and D, show the phenomenon of aggregation in low salt concentration (0.01 M), whereas and A and B, the slower species, do not.The buoyant density of the active species in our extract is the same as that of the purified enzyme; a high content of lipids seems therefore excluded.Species B in electric eel extracts (obtained after trypsic treatment) has been identified with the molecular form of the enzyme as recently purified and cristallized.This raises the question of the biological significance of this preparation, especially since one of the original species, A, has a smaller mass and is also converted into B during proteolysis.
Glutamate déshydrogénase
Authors: Pantaloni D. , Dessen P. 
Published: March 2005

The pig liver glutamic dehydrogenase has been studied by difference supectroscopy and shows two diphosphopyridine nucleotide binding sites per protomer of molecular weight 52000. A first NADH molecule binds on an adenylic site (Ka= 42 mM–1), and a second molecule on an nicotinamide site (Kn= 13 mM–1). NADPH binds only on the nicotinamide site (K= 21 mM–1).The adenylic site does not only strongly bind ADP (K= 2800 mM–1, but also ADP‐ribose, ATP, AMP, NADH, NAD, ApA, GpA, with a decreasing affinity; ApG and GTP does bind on this site which is specific of the adenosine 5′‐phosphate group. The high ionic strength decreases ADP binding.The linkage between the nicotinamide site and NADH induces a positive Cotton effect in the range of the absorption band of the reduced nicotinamide group; moreover the absorption spectra of bound NADH is shifted about 5 nm to the greater wavelengths with an hypochromism of 6%, with respect to free NADH.The evidence for two distinct binding sites is given by: (a) the existence of two difference spectra: the first due to the nicotinamide chromophore perturbation and the second due to the adenylic chromophore perturbation. This last is similar to that obtained with ADP, AMP, ATP; etc.; (b) the competition between ADP and NADH only on the adenylic site; (c) the fact that the saturation curves obtained from measurements made in the absorption range of adenosine and reduced nicotinamide chromophores are different and square with the theoretical saturation curves of two distinct sites per protomer.NAD also binds on the adenylic site in competition with ADP, whereas NADP and NADPH do not induce any perturbation of the adenosine chromophore.All these results are in good agreement with the interpretations given by Frieden to explain the effects observed in the steady‐state enzymatic kinetics at high concentrations of coenzyme.
The Specific Binding of Zinc(II) to Alkaline Phosphatase of Escherichia coli
Authors: Csopak H. 
Published: March 2005

The binding of Zn2+ to Escherichia coli alkaline phosphatase has been studied by pH titrations and equilibrium dialysis using 1,10‐phenanthroline as competing chelating agent.Measurements of the strength of binding under different experimental conditions have been performed:

At constant pH with different concentrations of chelating agent.
At different pH with constant concentration of chelating agent.
In the presence of denaturing agent at pH 8.0.

It was found on the basis of equilibrium dialysis experiments that the binding of the two zinc atoms to alkaline phosphatase may be described as coordination to the two equivalent and independent sites.The high values of the binding constants, and the fact that denaturation destroys the specific binding of zinc to alkaline phosphatase indicates chelate formation with the protein, unless some unknown prosthetic groups are involved.
Klassifizierung der Pullulanase als Exoenzym mit Hilfe der Gaschromatographie1
Authors: Wallenfels K. , Rached I. R. , Hucho F. 
Published: March 2005

Pullulanase from Aerobacter aerogenes is a glucosidase specifically splitting α‐1,6‐glycosidic bonds. A polymeric substrate for the pullulanase is the linear α‐glucan pullulan from Pullularia pullulans.This α‐glucan consists of maltotriose units linked together by α‐1,6‐glycosidic bonds. This means that the polysaccharide is degraded by pullulanase to yield exclusively maltotriose. There are two possibilities of enzyme action:a) either the hydrolysis starts from one end of the linear chain directly setting free maltotriose;b) or random splitting occurs to give larger units of varying molecular weight which will finally be degraded to maltotriose.The decision between these two alternatives could be made by gas liquid chromatography. The quantity of liberated maltotriose rises linearly with the reaction time, which proves that hydrolysis occurs from the end of the substrate chain. This method using gas liquid chromatography as an analytical tool may also be applied to monitor the action of other hydrolytic enzymes, as it could be shown for α‐ and β‐amylase.
Iodation des protéines par voie enzymatique
Authors: Nunez J. , Pommiter J. 
Published: March 2005

In the preceding publication we have shown that horse radish peroxidase forms an enzymehalogen complex with iodide; first the halogen is oxidised by the enzyme forming the complex; secondly the oxidised halogen is transfered directly from the complex to acceptor proteins. Therefore we have assumed that an interaction may occur between the enzyme‐halogen complex and the tyrosine residues of the protein acceptor.In the present work we will show that an enzyme‐protein complex can be formed; when horse radish peroxidase is incubated in the presence of both thyroglobulin and an H2O2 generating system, thyroglobulin isolated after the reaction is linked to peroxidase molecules. This complex is not formed when the H2O2 generating system is omitted. This result suggests that the tyrosine groups of thyroglobulin are oxidised by the peroxidase. Free tyrosine is indeed oxidised by the enzyme through a free‐radical mechanism; the fact that 50% of the radioactivity, present in the 3,5 positions is freed as tritiated water indicates that [3,5‐3H2]tyrosine forms a dimer during peroxidase oxidation. If free tyrosine is oxidised by such a mechanism we might assume that the residues of the same amino acid linked to a protein may be used as a substrate by the peroxidase. Such an assumption is supported by the fact that proteins are competitive inhibitors of the gaïacol peroxidative oxidation. If the tyrosine residues of the protein are oxidised as free radicals we might assume that the oxidised form of iodine linked to the enzyme is I. Therefore the mechanism of enzymatic iodination of proteins should proceed by an addition of free radicals.We can conclude from kinetic studies that the presence of an increasing amount of protein, up to a certain limit, inhibits the iodination reaction. Iodide inhibits only when it is present in excess, where I2 is formed. From these results we might propose the following mechanism for the iodination reaction: the enzyme contains two sites almost identical; each of them should be able to form the complex with one of the two substrates, sequentially; when iodide is linked first, the velocity of the reaction attains maximum; when the protein is linked prior to the first site, iodide linkage to the second site is slowed and the velocity of the reaction reduced.
Affinité pour la streptomycine des ribosomes d'Escherichia coli
Authors: Petitpas‐Dewandre A. , Barbason H. , Verly W. G. 
Published: March 2005

Ribosomes were isolated from four Escherichia coli K12 mutants, obtained by the action of ethyl methanesulfonate–with high (R) and low (r) resistance to streptomycin, dependent on high (D) and low (d) concentrations of streptomycin–and from the original sensitive strain (S). The ribosomal preparations were analyzed by sucrose‐gradient centrifugation, analytical ultra‐centrifugation, electron microscopy, determination of RNA to protein ratios, ability to synthesize polyphenylalanine in the presence of poly U, and the effect of streptomycin on this synthesis.The amounts of the antibiotic taken up by the ribosomes of the sensitive strain and of the mutants were determined for different concentrations of free [14C]streptomycin and the results plotted according to Scatchard's equation. The graphs show that each ribosome, in the mutants as well as in the sensitive strain, contains only one receptor site for one streptomycin molecule; as measured by the equilibrium constant of the reversible adsorption, the affinities of the binding site for the antibiotic are: S = 109 × 103; r = 13 × 103; R = 3.8 × 103; d = 42 × 103; D = 10 × 103.The observation that the ribosomes from the selected dependent mutants as well as those from the simply resistant ones have lower affinities for streptomycin than the ribosomes from the sensitive strain, could mean that the ribosomes from the resistant and the selected dependent mutants do not belong to different categories, and that E. coli dependence on streptomycin might have an extraribosomal origin.
Der Testosteronstoffwechsel in der isoliert perfundierten Meerschweinchenleber
Authors: Demisch K. , Staib W. 
Published: March 2005

Testosterone metabolism of the guinea pig was investigated on the isolated perfused liver. Eight experiments were carried out using four male and four female animals, respectively.We could isolate and quantitate seven metabolites which showed identical chromatographic behaviour with corresponding reference substances such as free steroids, steroid‐acetates and steroid‐trimethylsilyl‐ethers on thinlayer plates and on two different stationary phases during gas‐liquid‐chromatography.The identified metabolites constituted 73% of the radioactive material extractable by organic solvents after perfusion.The major part of the remaining 27% of radioactive material was found on the starting point of the first chromatogram. These metabolites are likely to be hydroxylated derivatives of dihydro‐ and tetrahydro‐testosterone because of their polar behaviour. Recently such metabolites could be identified.It was shown that the liver of the guinea pig hydroxylates testosterone and androstenedione mainly in position 6β‐ and 7α. The reductive metabolism of testosterone was very low. Only 3α‐hydroxy‐5β‐androstane‐17‐one and 3α,17β‐dihydroxy‐5β‐androstane were isolated in very small amounts. No metabolites giving evidence for 5α‐reductase activity were found.Sex differences in the metabolism of testosterone could not be demonstrated.
Biosynthesis and Metabolism of Hydroxyphenylacetic Acids in Higher Plants
Authors: Kindl H. 
Published: March 2005

2‐Hydroxyphenylacetic acid, a natural phenolic product found in the genus Astilbe, derives from the shikimic acid pathway via phenylpyruvic acid. The existence of two routes for the biosynthesis of 2‐hydroxyphenylacetic acid could be demonstrated:a) A direct transformation of phenylpyruvic acid into 2‐hydroxyphenylacetic acid involving a migration of the side chain. More than 95% of the tritium activity of 2‐hydroxyphenylacetic acid was localized in position 5 when l‐[4‐3H]phenylalanine was fed. This complex oxidation is analogous to the known conversion of 4‐hydroxyphenylpyruvic acid to homogentisic acid.b) A hydroxylation of [4‐3H]phenylacetic acid to [4‐3H]2‐hydroxyphenylacetic acid was observed in vivo, and was also found to take place in vitro utilizing the system peroxidaseendiol‐O2.
2,3‐Dihydroxyphenylacetic acid and 2‐hydroxy‐3‐methoxyphenylacetic acid could be established as natural products occurring in higher plants. Their chemical synthesis is described. By feeding experiments the following metabolic pathway is suggested: 2‐hydroxyphenylacetic acid → 2,3‐dihydroxyphenylacetic acid → 2‐hydroxy‐3‐methoxyphenylacetic acid. 3,4‐Dihydroxyphenylacetic acid and 3‐methoxy‐4‐hydroxyphenylacetic acid have been detected in extracts from various species of Astilbe and identified by paper chromatography. These two acids are metabolic products of 4‐hydroxyphenylacetic acid.
Experiments with [U‐14C]shikimic acid and dl‐[α‐14C]phenylalanine seem to indicate that the regulation of the biosynthesis of 2‐hydroxyphenylacetic acid and 4‐hydroxyphenylacetic acid takes place on the level of prephenic acid.
Preliminary results were obtained consistent with the hypothesis that in Astilbe chinensis the 2,3‐dihydroxyphenylacetic acid, 3,4‐dihydroxyphenylacetic acid and 2,5‐dihydroxyphenylacetic acid are further metabolized and can be degraded by ring cleavage.
Studies on the Morphopoiesis of the Head of Phage T‐Even
Authors: Kühl P. W. , Hofschneider P. H. 
Published: March 2005

Assembly of T4 polyheads and T4 phage has been investigated under special metabolic conditions of the host cell. The purpose of the investigation was to determine whether the assembly of polyheads or capsids depends on protein and DNA synthesis and whether it is energy requiring. The influences of chloramphenicol, 5‐fluoro‐2′‐deoxyuridine and potassium cyanide on the maturation process were studied. The main results of experiments performed with T4D.20 (amN50) and T4D.20(amN50)‐e are as follows:

The maturation of polyheads and capsids is independent of concurrent protein synthesis; if the protein synthesis is arrested 10 min after infection or later, the existing protein precursor pools can be depleted by 90%.
With phage DNA synthesis reduced to about 10%, the capsid assembly is diminished, but not that of polyheads. Capsids may, polyheads may not need DNA as a morphopoietic factor.
The assembly of polyheads, but not that of capsids is partially inhibited by cyanide which lowers the intracellular ATP level to 10–20%.
Biochemical Studies on Lipopolysaccharides of Salmonella R Mutants
Authors: Gmeiner J. , Lüderitz O. , Westphal O. 
Published: March 2005

The endotoxically active cell wall glycolipid of a highly deficient heptose‐less R mutant of Salmonella minnesota, consisting of 2‐keto‐3‐deoxyoctonic acid (KDO) and lipid A, was subjected to hydrazinolysis. Besides fatty acid hydrazides, a water‐soluble main fraction was obtained, containing KDO, glucosamine, and ester phosphate and free phosphorylethanolamine. The application of two procedures of partial hydrolysis, followed by paper electrophoretic separation, led to seven oligosaccharides.Their structures were evaluated with the aid of the following analytical methods: further acid degradation, borohydride reduction, ninhydrin degradation, the Morgan‐Elson reaction, treatment with phosphomonoesterase and N‐acetylglucosaminidases. The results show that the backbone of lipid A contains phosphorylated glucosaminyl→glucosamine disaccacharide units, probably linked β‐1,6, to which a trisaccharide composed of three KDO residues is linked ketosidically to form a pentasaccharide which appears to be a common structure in many Enterobacteriaceae.
Zur Bildung von Chinolinalkaloiden in Pflanzen
Authors: Luckner M. , Winter K. , Reisch J. 
Published: March 2005

Cyclopenase, an enzyme from the mycelium of Penicillium viridicatum Westling and Penicillium cyclopium Westling catalyses the transformation of the benzodiazepine derivatives (–)‐cyclopenine and (–)‐cyclopenol to the quinoline derivatives viridicatine and viridicatol, respectively. This rearrangement, which is connected with the elimination of molar amounts of CO2 and methylamine takes place in an nonenzymatic process too, if (–)‐cyclopenine and (–)‐cyclopenol are treated with acids or Lewis acids. In anhydrous medium instead of CO2 and methylamine, methylisocyanate is obtained. 14CO2 is formed from (–)‐[5‐14C]cyclopenine either by the enzyme or by the acid‐catalysed transformation, the viridicatine being inactive (Table). In experiments with 2H2O or H218O as solvents neither the cyclopenase nor the acid‐catalysed rearrangement proceeded with a significant incorporation of 2H or 18O (Fig. 1).These experimental results indicate that:a) enzymatic and nonenzymatic transformations of the investigated benzodiazepines to the corresponding quinoline derivatives proceed by similar mechanisms,b) closure of the hetero‐ring of the quinoline moiety involves C‐atoms 5a and 10 of the benzodiazepine compounds andc) the hydroxyl group in position 3 of the quinoline ring is derived directly from the epoxide oxygen.In Scheme 1 a possible reaction sequence for the transformation is given.
Beziehung zwischen Lipolyse, Gluconeogenese und Insulinsekretion nach Cortisolgabe an Ratten
Authors: Herrmann J. , Staib W. 
Published: March 2005

Plasma concentrations of free fatty acids, free glycerin, glucose, immunologically measurable insulin and insulin‐like activity have been studied 0.5–6 h after oral application of 5 mg cortisol/100 g body weight to 24 h starved intact rats.Free fatty acids decrease significantly within 30 min in comparison with controls and then rise up to a maximum after 4 h; the 4 h value was not statistically different from the controls.In contrast to control animals blood sugar already shows a significant rise at 2 h. Concentrations of free fatty acids and free glycerin showed no evidence for a cortisol stimulated lipolysis. Therefore and in connection with some theoretical considerations it seems rather improbable that lipolysis products are of any essential importance either as substrates or as regulators in cortisol‐dependent gluconeogenesis.Immunologically measurable insulin decreases within 1 h after cortisol application (P < 0.05) and reaches a minimum after 2 h which differs from controls with P < 0.001. Insulin‐like activity measured at epididymical adipose tissue showed a similar course with a decrease at 2 h followed by a rise up to the 6 h value.A significant decrease of plasma insulin concentration could also be found in cortisol treated adrenalectomized rats.After hypophysectomy an effect of cortisol on plasma insulin concentration could no longer be detected.Experiments with the isolated perfused rat pancreas show that after glucose stimulation, cortisol does not significantly influence either basal insulin secretion or insulin release. The decrease of plasma insulin concentration of cortisol treated animals can not be explained by a direct inhibition on the interalveolar cell islets by cortisol.From the different influence of cortisol on the insulin liberation in intact animals, as well as in adrenalectomized ones on the one hand and in hypophysectomized on the other, it is concluded that the observed cortisol effect is mediated by insulotropic adenohypophysis hormones. This view is supported by the fact that a direct influence of the steroid on Langerhans' cells could be excluded by pancreas perfusion.
Enzymic Epimerization of Sequoyitol to d‐Pinitol in Trifolium incarnatum
Authors: Ruis H. , Hoffmann‐Ostenhof O. 
Published: March 2005

The partial purification of an enzyme system from Trifolium incarnatum catalyzing the epimerization of sequoyitol to d‐pinitol and its characterization is described. The reaction proceeds via a keto intermediate, d‐5‐O‐methyl‐2,3,5/4,6‐pentahydroxycyclohexanone, and is catalyzed by two dehydrogenases or one protein with two dehydrogenase actions, of which the first one is NAD‐specific and oxidizes sequoyitol to the keto intermediate, whereas the other has the function to reduce the keto compound to d‐pinitol using NADPH as hydrogen donor. Both dehydrogenase actions as well as the overall epimerization reaction were shown to be reversible.Although the sequoyitol dehydrogenase activity can be easily destroyed by several means which leave the d‐pinitol dehydrogenase activity intact, no real separation of the two activities has been achieved. The protein or proteins responsible for the two activities have a molecular weight of about 34,000 as determined by the gel filtration method.The two activities do not only differ in their sensitivity towards inhibitors, their substrate and coenzyme specificities, but also in their stereospecificity with respect to the coenzymes. Whereas the NAD‐specific sequoyitol dehydrogenase activity is B‐specific, the NADP‐specific d‐pinitol dehydrogenase activity shows A‐specificity. On the basis of these findings, a possible mechanism for the epimerization is discussed.