bluuebunny/crossref_metadata_2025_split huggingface dataset:
Size, Complexity and Abundance of a Specific Poly(A)‐Containing RNA of Liver from Male Xenopus Induced to Vitellogenin Synthesis by Estrogen
Authors: WAHLI Walter , WYLER Toni , WEBER Rudolf , RYFFEL Gerhart U. 
Published: March 2005

Estrogen treatment of Xenopus males leads to the appearance of a new species of poly(A)‐containing RNA in the liver, at a stage when large amounts of the estrogen‐induced yolk precursor protein, vitellogenin, is produced. This estrogen‐induced RNA sediments at 28 S and migrates on gels in aqueous solution with an apparent molecular weight of 2.0 × 106. Contour length measurements under denatiuring conditions in the electron microscope reveal a molecular weight of 2.34 × 106 compared to the mouse 28‐S rRNA.Labeling experiments show that the estrogen‐induced RNA has a higher stability than the average liver poly(A)‐containing RNA and represents 10–20% of the poly(A)‐containing RNA in the cytoplasm after 24 h of labeling.Hybridization of complementary DNA, synthesized on the. isolated estrogen‐induced RNA, with its template suggests a complexity corresponding to a single species of poly(A)‐containing RNA of such a high molecular weight. Hybridization of the complementary DNA with cytoplasmic poly(A)‐containing RNA from estrogen‐treated Xenopus males and control toads show that the estrogen‐induced RNA constitutes 12–15% of all cytoplasmic poly(A)‐containing RNA, and is at least 2000‐fold less abundant in untreated males.Size, complexity and abundance of the estrogen‐induced RNA are characteristics expected for a mRNA coding for vitellogenin.
Affinity Chromatography and Binding Studies on Immobilized Adenosine 5′‐Monophosphate and Adenosine 2′,5′‐Bisphosphateof Nicotinamide Nucleotide Transhydrogenasefrom Pseudomonas aeruginosa
Authors: HÖJEBERG Bo , BRODELIUS Peter , RYDSTRÖM Jan , MOSBACH Klaus 
Published: March 2005

Nicotinamide nucleotide transhydrogenase from Pseudomonas aeruginosa was purified to apparent homogeneity with an improved method employing affinity chromatography on N6‐(6‐aminoyl)‐adenosine‐2′,5′‐bisphosphate‐Sepharose 4B.
Polyacrylamide gel electrophoresis of the purified transhydrogenase carried out in the presence of sodium dodecyl sulphate, indicated a minimal molecular weight of 55000 ± 2000.
The kinetic and regulatory properties of the purified transhydrogenase resembled those of the crude enzyme, i.e., NADPH, adenosine 2′‐monophosphate and Ca2+were activators whereas NADP+ was inhibitory.
Nicotinamide nucleotide‐specific release of binding of the transhydrogenase to N6‐(6‐aminohexyl)‐adenosine‐2′,5′‐bisphosphate‐Sepharose and N6‐(6‐aminohexyl)‐adenosine‐5′‐monophospliate‐Sepharose suggests the presence of at least two separate binding sites for nicotinamide nucleotides, one that is specific for NADP(H) and one that binds both NAD(H) and NADP(H).
Binding of transhydrogenase to N6‐(6‐aminohexyl)‐adenosine‐2′,5′‐bisphosphate‐Sepharose and activation of the enzyme by adenosine‐2′,5′‐bisphosphate showed a marked pH dependence. In contrast, inhibition of the Ca2+‐activated enzyme by adenosine 2′,5′‐bisphosphate was virtually constant at various pH values. This discrepancy was interpreted to indicate the existence of separate nucleotide‐binding effector and active sites.
Phosphorylation of Intracellular Fructose in Bacillus subtilis Mediated by Phosphoenolpyruvate‐l‐Fructose Phosphotransferase
Authors: DELOBBE André , CHALUMEAU Hervé , CLAVERIE Jean‐Michel , GAY Philippe 
Published: March 2005

Intracellular fructose provided by the sorbitol pathway in Bacillus subtilis, can be phosphorylated by the phosphoenolpyruvate‐1‐fructose phosphotransferase which is known to mediate a vectorial metabolism. The fate of this intracellular fructose was studied using mutants lacking either the fructose 1‐phosphate pathway or the fructose 6‐phosphate pathway.It was shown that the phosphoenolpyruvate‐dependent phosphorylation needs a prior exit of the sugar into the medium, this exit being probably catalysed by a transport system. A low affinity intracellular phosphoenolpyruvate phosphotransferase system was found, which seems to be devoid of a physiological role.
Spatial Characteristics of the Aspartate Membrane Carrier and Its Relationship to the Glutamate Transport System in Membrane Vesicles of Escherichia coli K‐12 Cavalli
Authors: KAHANE Simona , METZER Esther , HALPERN Yeheskel S. 
Published: March 2005

Membrane vesicles of Escherichia coli K‐12 CS7, a strain genetically derepressed for glutamate permease, maintain low aspartate transport activity, like that of preparations of the wild‐type parent. Growth of the parent CS101 on aspartate as the source of carbon or nitrogen results in derepression of both aspartate and glutamate transport. Growth of strain CS7 on aspartate derepresses aspartate transport to the same extent as in strain CS101, but only slightly increases the derepressed level of glutamate transport activity.
The affinity of the membrane transport system for glutamate is enhanced by sodium, while that for aspartate is not.
Although the affinities for glutamate (23 μM) and aspartate (12 μM) are similar, aspartate does not inhibit glutamate transport, while glutamate competitively inhibits aspartate transport.
Aspartate transport, but not glutamate transport, is competitively inhibited by C4 dicarboxylic acids, whereas 2‐oxoglutarate competitively inhibits glutamate transport, but not aspartate transport.
Competitive inhibition of l‐aspartate transport by l‐glutamate and by the 5‐methyl ester of l‐glutamate is abolished in the presence of 2‐oxoglutarate. However, 2‐oxoglutarate does not affect the competitive inhibition of l‐aspartate transport by d‐aspartate and by dl‐threo‐3‐hydroxyaspartate. The relationship between the two dicarboxylic amino acid transport systems and the spatial characteristics of the aspartate carrier are discussed in the light of these findings.
Nicotinamide‐Dependent One‐Electron and Two‐Electron (Flavin) Oxidoreduction : Thermodynamics, Kinetics, and Mechanism
Authors: BLANKENHORN Gunter 
Published: March 2005

Biological nicotinamide‐dependent oxidoreduction consists of reversible 2e‐oxidoreduction of substrates. A mechanism involving subsequent le‐steps is shown to be very unfavourable due to the high energy of the nicotinamide radical.Free energy relationships provide a convenient tool, allowing one to differentiate between hydride transfer and hydrogen atom transfer. It is concluded that biological nicotinamide‐dependent, as well as flavin‐nicotinamide oxidoreduction, proceed via hydride transfer but not via hydrogen atom transfer.In flavin‐nicotinamide oxidoreduction, flavin‐nicotinamide charge transfer complexes are very likely the catalytic intermediates, preceding transfer of hydride ion. The energy of the long‐wavelength charge transfer transition of zwitterionic oxidized‐nicotinamide/reduced‐flavin complexes is strongly dependent on polarity. It is maximal in a highly polar environment.5‐Deazaflavins show the high thermodynamic radical instability of nicotinamides. They have to be considered as nicotinamide analog 2e‐oxidoreductants rather than flavin analogs, therefore, lacking the ability to catalyze reversible le‐oxidoreduction, essential for many flavoenzymes.
The Energetics of Escherichia coli during Aerobic Growth in Continuous Culture
Authors: FARMER Ian S. , JONES Colin W. 
Published: March 2005

The energetics of Escherichia coli W growing aerobically in continuous culture have been investigated. Conditions were chosen such that growth was limited by the availability of carbon or oxygen (energy‐limited cultures), or of ammonium or sulphate ions (excess energy cultures).
Under glycerol‐limited conditions YmaxO2(true molar growth yield with respect to oxygen) and YmaxATP (true molar growth yield with respect to ATP equivalents) were 50.9 g cells · mol O2−1 and 12.7 g cells mol ATP equivalents−1 respectively; these values were not substantially altered during growth limited by oxygen. ammonium or sulphate. In contrast, M (the energy requirement. for maintenance purposes) increased from approximately 2 mmol ATP equivalents · h−1 g.cell−1 during energy‐limited growth to 16.8 and 30.8 mmole ATP equivalents h−1 g cells−1 when growth was limited by ammonium and sulphate ions respectively.
Replacement of glycerol by other limiting carbon sources caused YmaxATP to alter within the range 13.9 (glucose) to 7.1 (acetate) g cells mol ATP equivalents−1 in the order glucose > galactose > arabinose > fructose > glycerol > fumarate > lactate > pyruvate > acetate. In each case the experimental value of YmaxATP was ≤ 55% of the theoretical value calculated from the known energy requirements for the biosynthesis of cell materials.
It is concluded from these results that neither M nor YmaxATP are constant values for E. coli. M varies with the energy supply, being highest under excess energy growth conditions where it may reflect energy wastage by the cell. On the other hand, YmaxATP varies with the nature of the growth substrate and thus reflects the different energy requirements for the synthesis of cell material from different carbon sources
Structure‐Activity Relationships in Acetylcholinesterase Reactions
Authors: JÄRV Jaak , KESVATERA Tônu , AAVIKSAAR Aavo 
Published: March 2005

The Michaelis‐Menten parameters kcat Ks(app) and the second‐order rate constants k11= k2/Ks of acetylcholinesterase‐catalyzed hydrolysis of 25 acetic esters with note‐ionic leaving groups have been determined at 25 °C and pH 7.5 in 0.15 M KCL A linear relationship between the substrate non‐covalent binding capacity and the leaving group hydrophobicity, and a multiparameter correlation of the acetylation reaction rate constant logarithm with the leaving group, inductive effect, hydrophobicity, and steric effect, have been established. The acetyl‐enzyme deacetylation rate constant has been calculated. Taken together, a fairly complete understanding of acetylcholinesterase specificity is possible.The data are consistent with a model of the acetylcholinesterase active site, in which the catalytically active groups are located at the bottom of a jaws‐like slit with a limited range of hydrophobic walls that provide the sorption of the substrate leaving groups not longer than that in n‐butyl acetate.
The Transfer of J Blood‐Group Activity from J‐Containing Bovine Serum to J‐Negative Erythrocytes
Authors: KRÖTLINGER Franc , THIELE Otto Wolfgang , OHL Cornelia 
Published: March 2005

The J blood‐group activity of bovine serum is contained both in a lipid and in a nonlipid fraction. This is also true for calf serum.It is demonstrated that the J determinant is transferred from a serum protein onto the erythrocyte membrane by incubation in vitro. Even though the donor of J activity is a lipid‐free serum protein (probably a glycoprotein), the transferred J activity is detectable only in the lipid fraction of erythrocytes. Thus, the J determinant (probably a carbohydrate unit) must have been detached from a serum glycoprotein and transferred to a lipidic receptor (probably a glycosphingolipid) at the erythrocyte membrane.It is suggested that an enzyme system located in or at the erythrocyte membrane is responsible for the transfer of J substance.The transfer of J substance is inhibited by a polar lipid present in bovine serum.
Diglyceride Kinase Activity of Microtubules
Authors: DALEO Gustavo R. , PIRAS Marta M. , PIRAS Romano 
Published: March 2005

Vinblastine‐isolated microtubule protein from chick embryonic muscles has an enzymatic activity which catalyzes the formation of phosphatidic acid from diglycerides and ATP. The pH optimum (6.4), sedimentation on sucrose gradients (Mr= 85000), and sensitivity to ions of this diglyceride kinase activity are different to those of a similar enzymatic activity present in 150000xg supernatants of chick embryonic muscle homogenates, suggesting that it is a different species which is associated specifically with the microtubules. The reaction requires a divalent ion (e.g. 0.4 mM Mg2+ gives half‐maximal stimulation), and GTP can replace ATP rather effectively, especially at nucleotide concentrations lower than 50 μM. The sedimentation of the diglyceride kinase on sucrose gradients coincides with that of the microtubules‐associated protein kinase (Mr= 75000): the heat‐stability and sensitivity to proteolysis of both activities are also very similar. Stimulation of one reaction by the addition of the corresponding exogenous substrate does not impair the phosphorylation of the other, and no radioactivity is lost from phosphatidic acid or the protein moiety upon incubation of pre‐labelled microtubules with a large excess of unlabelled ATP or GTP.In addition to diglyceride kinase and protein kinase activities (0.2 and 0.3 nmol 32P‐transferred × min−1× mg−1 microtubular protein, respectively), microtubules also contain an associated ATPase (2.8 nmol × min−1× mg−1), which requires either Mg2+ or Ca2+, can hydrolyze GTP quite effectively, and sediments with a molecular weight of 95000.The results obtained are discussed in connection with the possible relationships existing among these enzymatic activities, as well as their probable role in microtubular functions.
Initiation of the Polypeptide Chain by Reticulocyte Cell‐Free Systems
Authors: FRESNO Manuel , CARRASCO Luis , VAZQUEZ David 
Published: March 2005

In order to elucidate the mechanism of action of inhibitors that block the initiation of protein synthesis in mammalian systems, we have studied the following steps: (a) formation of the ternary complex Met‐tRNAf IF‐E2 GTP, (b) binding of the initiator Met‐tRNAf to the 40‐S ribosomal subunit in the presence of initiation factors and dependent or not on the addition of mRNA, (c) formation of the initiation complex with 80‐S ribosomes and (d) formation of the first peptide bond.Adrenochrome, aurintricarboxylic acid, polydextran sulphate, pyrochatechol violet and showdomycin block the formation of the ternary complex Met‐tRNAf· IF‐E2 GTP. Edeine A1, aurintricarboxylic acid and polydextran sulphate block the binding of the mRNA to the 40‐S ribosomal subunit. Pactamycin induces the formation of stable smaller initiation complexes which are unable to go through the subsequent steps of initiation. Stimulation of the binding of the initiator Met‐tRNAf to the 80‐S ribosome in the presence of initiation factors is observed with sparsomycin and antibiotics of the sesquiterpene family (verrucarin A, trichodermin and trichothecin). However, these antibiotics block the reaction of the bound Met‐tRNAf with puromycin. Narciclasine has no effect on the binding of the initiator to the ribosome but strongly blocks its reaction with puromycin.We have developed a simple technique to detect the Met‐tRNAf· 40‐S‐subunit poly(A,G,U) initiation complexes by chromatography on Sepharose 6B columns. The requirements for the formation of such complexes measured by this technique and its comparison with the sucrose gradient centrifugation method are described.
Role of GTP in Eukaryotic Polypeptide‐Chain Initiation
Authors: OCHIAI‐YANAGI Sonoe , MAZUMDER Rajarshi 
Published: March 2005

A factor, which makes a ternary complex with GTP and eukaryotic initiator tRNA (Met‐ tRNAi), has been purified 100‐fold from developed cysts of Artemia salina. Some of the properties of the purified factor have been studied.
Mg2+ appears to inhibit ternary complex formation.
Little or no ternary complex is formed when 5 μ GTP is replaced by an identical concentration of UTP, CTP or ATP. The analog, guanosine 5′‐(β,γ‐imino)triphosphate [GMP‐P(NH)P] seems to be a much better substitute for GTP than guanosine 5′‐(β,γ‐methylene)triphosphate [GMP‐ P(CH2)P]. Since GMP‐P(NH)P is as effective as GTP in ternary complex formation, it would appear that GTP plays the role of an allosteric effector in this step of eukaryotic polypeptide chain initiation.
GDP inhibits both the rate and extent of ternary complex formation. The inhibition is largely reversed by adding a 5‐fold molar excess of GTP over GDP. dGDP is slightly less inhibitory than GDP. UDP and CDP are much less inhibitory than GDP and very little inhibition is obtained with ADP.
The preformed ternary complex is rapidly and completely destroyed in the presence of N‐ethylmaleimide. The results suggest that free –SH groups of the factor may be essential for maintaining the integrity of the ternary complex.
Effects of Thyroid Hormone Deficiency on the Distribution of Hepatic Metabolites and Control of Pathways of Carbohydrate Metabolism in Liver and Adipose Tissue of the Rat
Authors: BAQUER Najma Zaheer , CASCALES Maria , McLEAN Patricia , GREENBAUM A. Leslie 
Published: March 2005

Measurements have been made of the hepatic metabolites in normal and thyroidectomized rats and of enzymes of the glycolytic route, the pentose phosphate pathway, the tricarboxylic acid cycle and of lipogenesis together with the flux of glucose through alternative pathways of glucose metabolism and into lipid.
There is a significant fall in the content of ADP, AMP, citrate, long‐chain acyl‐CoA derivatives and a rise of 3‐phosphoglycerate, 2‐phosphoglycerate and phosphoenolpyruvate following thyroidectomy. The observed changes in the glycolytic intermediates may be correlated with the increased activity of phosphofructokinase relative to pyruvate kinase and fructose bisphosphatase.
The NAD+/NADH quotient of the mitochondrial compartment, calculated from the reactants and Keq of 3‐hydroxybutyrate dehydrogenase, becomes significantly more oxidized in hypothyroid animals. The redox state of the cytosolic NAD and NADP couples remains relatively unchanged.
The changes in the hepatic content of CoA derivatives and citrate and in the mitochondrial redox state are interpreted as indicating a depressed rate of lipid oxidation.
Calculations of the compartmentation of metabolites between the cytosol and mitochondria indicate a very marked decrease in mitochondrial citrate, 2‐oxoglutarate and glutamate with smaller changes in aspartate and malate. These changes are interpreted as providing evidence for the importance of modifications in the malate‐aspartate shuttle in hypothyroidism; this is further supported by measured changes in the distribution and activities of the component enzymes of the hydrogen shuttles.
There is a diminished activity of glucokinase and of enzymes of the glycolytic pathway below phosphofructokinase in livers from hypothyroid rats. The oxidative enzymes of the pentose phosphate pathway, ATP‐citrate lyase, ‘malic’ enzyme and fatty acid synthetase also decrease markedly. There is a striking parallelism between the changes of enzyme profile of liver and adipose tissue in hypothyroidism.
Adrenal glands from hypothyroid rats showed a generalized decline in enzyme activity in parallel with the fall in tissue weight. Cytosolic glycerol‐3‐phosphate dehydrogenase decreased sharply.
The present results are discussed in relation to data in the literature on the increased activities of cyclic AMP and cyclic GMP phosphodiesterases in hypothyroidism, observations which integrate the relationships between anabolic and catabolic pathways of carbohydrate and lipid metabolism with alterations in hormone sensitivity in hypothyroidism.
Controlled Proteolysis of Flavocytochrome b2
Authors: POMPON Denis , LEDERER Florence 
Published: March 2005

It is known that each subunit of the tetrameric flavocytochrome b2 can be cleaved by yeast proteases to fragments of molecular weight 33‐36000 and 21000, with some modification of catalytic properties, but without destruction of the oligomeric state of the protein. We report here experimental conditions which enabled us to simulate this specific cleavage in a controlled fashion with chymotrypsin and subtilisin. With trypsin and papain, on the other hand, it was not found possible to stop the digestion in such a way as to obtain a homogeneous still active product. A characterization of the enzymatic forms obtained by digestion with chymotrypsin and subtilisin at 0 °C shows that modification of enzymatic and solubility properties occurs in a stepwise fashion. It is also concluded that cleavage by yeast proteases is accompanied by loss of 10 to 25 residues.At 37 °C, chymotrypsin digestion yields a heme‐binding core of molecular weight 15000, larger than the already characterized tryptic heme‐binding core by about 40 residues. Although the latter is known to be very similar to trypsin‐solubilized cytochrome b5, the lack of aggregation of the former in aqueous solution, its amino acid composition and circular dichroism spectra do not point to a similarity of its additional peptide segment with the hydrophobic tail of detergent‐solubilized cytochrome b5.
Taipoxin, an Extremely Potent Presynaptic Neurotoxin from the Venom of the Australian Snake Taipan (Oxyuranus s. scutellatus)
Authors: FOHLMAN Jan , EAKER David , KARLSSON Evert , THESLEFF Stephen 
Published: March 2005

Taipoxin (taipan toxin), purified from the venom of the Australian taipan (Oxyuranus s. scutellatus) by gel filtration on Sephadex G‐75 followed by column zone electrophoresis, is the most lethal neurotoxin yet isolated from any snake venom. The LD50 is 2 μg/kg in the mouse. The main physiological effect is a gradual reduction to complete stop of evoked and spontaneous release of acetylcholine from motor nerve terminals. Intoxicated animals die of asphyxia caused by neuromuscular blockage of the respiratory muscles.Taipoxin is a moderately acidic sialo‐glycoprotein (pI 5) with a molecular weight of 45600 as calculated from composition data or 46800 as determined by meniscus depletion sedimentation equilibrium. Taipoxin is a 1:1:1 ternary complex of subunits designated α, β and γ which dissociate completely at low pH and high ionic strength or in 6 M guanidine hydrochloride. The dissociation by guanidine at neutral pH is reversible, while the acid‐induced dissociation is not. The α and β components consist of 120 amino acid residues cross‐linked by seven disulfide bridges, whereas the component has 135 residues and eight disulfides.The very basic (pI < 10) a component contains 13 residues of arginine and is the only subunit displaying lethal neurotoxicity (mouse LD50∼ 300 μg/kg): The neutral β fraction was separated by ion‐exchange chromatography into two iso‐component, β1 and β2, which differ slightly in amino acid composition. The very acidic γ component contains all of the carbohydrate, which includes 4‐5 residues of sialic aid. The three subunits are homologous in sequence although the γ component is eight residues longer on the N‐terminus and must also contain extra amino acids elsewhere