bluuebunny/crossref_metadata_2025_split huggingface dataset:
Binding of Analogues of the Antibiotics Distamycin A and Netropsin to Native DNA
Authors: Zimmeer Christoph , Luck Gerhard , Thrum Heinz , Pitra Christian 
Published: March 2005

Binding effects of DNA with two distamycin A analogues containing four and five 1‐methyl‐pyrrole residues (distamycin A contains three of these residues) and with a degradation product of netropsin have been investigated by ultraviolet absorbance, melting and circular dichroism measurements.Increasing numbers of the methylpyrrole groups (3 to 5) enhance the thermal stability of the oligopeptide complex. On the other hand elimination of the basic groups of the netropsin molecule decreases the melting temperature of the oligopeptide · DNA complex enormously. The circular dichroism spectrum of DNA is also less affected by the degradation product compared to netropsin. Circular dichroism spectra of the complexes exhibit a pronounced band at the longer wavelength region and indicate an increasing chirality in the complex with increasing number of chromophores of the oligopeptides.From the results it is concluded that electrostatic attraction of the oligopeptides by interaction of the propionamidino and guanidino groups with the negative phosphate sites of DNA is important for the formation of the complex. However, non‐ionic forces, which have been discussed earlier, seem to be involved and may be attributed to the chromophore residues oriented in the helical grooves.The different binding tendency of the oligopeptides with DNA is discussed together with the biological activity of the oligopeptides.
The Pathway of Glutamate Oxidation in Rabbit Reticulocytes
Authors: Rost Johann , Rapoport Samuel M. 
Published: March 2005

It is shown by means of experiments on intact cells with 14C‐labelled substrates that the first step in the oxidative metabolism of glutamate in rabbit‐reticulocytes is a transamination with oxaloacetate to form aspartate.
The aspartate is metabolized further in such a manner that CO2 is formed from all C‐atoms. With tracer amounts of glutamate no accumulation of aspartate occurs, in contrast to isolated mitochondria. The mechanism of the utilization of aspartate appears to be a decarboxylation of oxaloacetate to pyruvate, which is the main reaction of oxaloacetate under conditions of loading with glutamate.
On account of the minute contribution of the amino group of glutamate to the ammonia formation, which in itself is smaller than expected from the CO2 formation, an acceptor for the amino group of amino acids is postulated.
Aminoacylation of Fragment Combinations from Yeast tRNAPhe
Authors: Thiebe Rainer , Harbers Klaus , Zachau Hans G. 
Published: March 2005

The aminoacylation of 15 fragments from yeast tRNAPhe and of various mixtures of these fragments was studied in detail. The aminoacylation conditions were systematically varied in order to obtain maximal incorporation of phenylalanine.
No fragment by itself accepted phenylalanine.
Fragment combinations in which parts of the anticodon loop or the dihydrouridine loop were missing, accepted phenylalanine to an extent of 20–75% compared to intact tRNAphe. Modifications in both regions together inactivated the molecule. With the anticodon stem and/or the minilooop missing, low but significant activity was found. Splits in the dihydrouridine loop and in the T‐Ψ‐C loop together did not abolish the phenylalanine acceptance. Combinations in which parts of the dihydrouridine stem or of the T‐Ψ‐C stem were missing could not be amino‐acylated.
Complete association of complementary fragments was observed in all cases. The results of charging and heating experiments, however, indicate the coexistence of different fragment combinations in a fragment mixture. The incomplete aminoacylation of fragment mixtures is explained by the presence of fragment combinations with an unsuitable three‐dimensional structure.
The rate of aminoacylation was lower for fragment combinations than for tRNAPhe. The Michaelis constants of 3 fragment combinations were identical to the one of tRNAPhe. Two fragment mixtures inhibited the rate of charging of tRNAPhe.
Phenylalanine was the only amino acid which was accepted by the fragment mixtures with synthetases from yeast or Escherichia coli. No mischarging was observed.
The results together with those of related publications are discussed with respect to recognition sites of tRNAPhe for the cognate synthetase.
Caractérisation des variants génétiques des caséines αsl et β bovines
Authors: Grosclaude François , Mahé Marie‐Françoise , Mercier Jean‐Claude , Ribadeau‐Dumas Bruno 
Published: March 2005

The three major casein species of cow's milk are known to show a genetic polymorphism: four variants of αsl‐casein (A, B, C, D), five of β‐casein (A1, A2, A3, B, C) and two of χ‐casein (A, B) have been discovered until the present time in the western breeds of cattle (Bos taurus) (see review by Aschaffenburg [1]). These variants, whose relative mobilities in gel electrophoresis at pH 8.6 and at pH 3.0 are shown in Fig.1, represent markers of the structural loci synthesizing the three casein species (αsl‐Cn, β‐Cn and χ‐Cn).The salient feature of the genetics of cattle caseins lies in the very close linkage of these three loci, which are likely to be clustered on the chromosome [2–5]. As a consequence of this close linkage, associations of αsl‐, β‐and χ‐casein variants are transmitted en bloc, as “gene complexes”. Our interpretation of available data on the frequencies of the gene complexes in cattle populations had led us to propose a phylogeny of the genetic variants of αsl‐and β‐caseins, and also to suggest that the mutation sites corresponding to the more common ones are particularly close together on the chromosome [6]. These hypotheses prompted us to identify and to position the alterations specific for each of the variants of αsl‐ and β‐caseins.We have already, in recent publications, characterized the αslC, αslA and βA3 variants [7–9].The present work, which in the case of β‐casein was guided by indications on amino‐acid substitutions given by Pion et al. [10], Peterson et al. [11], Groves and Gordon [12], and which refers to the sequences of αsl B and βA2 caseins recently established by Mercier et al. [13] and Ribadeau‐Dumas et al. [14], deals with the four other variants, αslD, βA1, βB, βC.The variant αsl D differs from αsl B in that the alanyl residue in position 53 of the polypeptide chain is replaced by a phosphothreonyl residue (53 Ala → ThrP). There is no serine → proline substitution as previously proposed [15].Compared to βA2, the three variants βA1, βB and βC all differ by a 67 Pro → His substitution.In βB, in addition to the 67 Pro → His substitution, the seryl residue in position 122 is replaced by an arginyl residue, as previously mentioned [16].In βC, in addition to the 67 Pro → His substitution, the glutamyl residue in position 37 is replaced by a lysyl residue, and the seryl residue in position 35 is no more phosphorylated.Table 3 summarizes our results on all the genetic variants of αsl‐ and β‐caseins. These results make it possible to deduce phylogenic relationships (Fig. 6) that support and expand our former hypotheses [6]. The concept that the initiator end of β‐Cn locus is contiguous to the terminal end of αsl‐Cn locus accounts for the rare occurrence of recombinant types between αsl‐Cnc and β‐CnA1, β‐CnB, β‐CnC, since the distances between the corresponding mutation sites would be only 73, 128 and 43 codons, respectively.
Role of the Redox State in Ethanol‐Induced Suppression of Citrate‐Cycle Flux in the Perfused Liver of Normal, Hyper‐ and Hypothyroid Rats
Authors: Lindros Kai O. 
Published: March 2005

The mechanism of the ethanol‐induced suppression of the citric acid cycle has been studied by single‐passage perfusion of livers from normal, triiodothyronine‐treated and propylthiouraciltreated rats.
Ethanol oxidation increased the lactate/pyruvate ratio in the perfusion medium to about 50 and depressed the 14CO2 formation from [1‐14C]acetate and [1‐14C]hexanoato (taken to reflect citrate cycle flux) by 67% and 60%, respectively, in normal livers. In the livers of the hyperthyroid animals ethanol suppressed [1‐14C]acetate oxidation by 22% and [1‐14C]hexanoate oxidation by 34%, and the lactate/pyruvate ratio was only increased to about 20. In the hypothyroid group ethanol enhanced the lactate/pyruvate ratio slightly more than in the controls and suppressed the oxidation of acetate and hexanoate by 79 and 62%, respectively.
Hepatic ethanol elimination was slightly slower in the hyper‐ and hypothyroid groups than in the controls. Hexanoate (1 mM) stimulated oxygen uptake in all groups but inhibited ethanol oxidation by 45% in the hyperthyroid group and only by 18% in the hypothyroid group. Pyruvate, on the other hand, stimulated ethanol elimination only slightly in the hyperthyroid group, by about 50% in the controls and by about 70% in the hypothyroid group.
Oxidation of acetate and hexanoate was also depressed by acetaldehyde. This effect was potentiated by pyrazole, which blocked the reduction of acetaldehyde and caused an increased shift in the lactate/pyruvate ratio, thus indicating that acetaldehyde also affects the citric acid cycle by causing a shift in the redox state.
A highly significant correlation was observed between the effect of ethanol on the output of 14CO2 from the labelled substrates and the shift in the lactate/pyruvate ratio. Experiments with different input levels of lactate and pyruvate demonstrated that the citric acid cycle is susceptible to the fall in pyruvate resulting from the shift in the redox state during ethanol oxidation.
Ribosomal Subunits from Rat Liver
Authors: Reboud Anne‐Marie , Arpin Monique , Reboud Jean‐Paul 
Published: March 2005

Ribosomal subunits from rat liver were prepared with a mild method which consisted of centrifuging ribosomes through a sucrose layer containing 0.3 M KCl. Isolated 40‐S subunits were obtained completely pure and 60‐S subunits were contaminated by less than 5% of 40‐S. In the presence of Mg2+ subunits reassociated into monosomes, which had high activity in polyphenylalanine synthesis. 40‐S, but not 60‐S, subunits could bind [3H]poly(U) and [14C]phenylalanyl‐tRNA.Both subunits could be lyophilized and then kept at room temperature without detectable change in activity nor in sedimentation profile.Determination of the chemical composition of both subunits showed that 40‐S had a higher protein content than 60‐S subunits. However concentrated‐salt washings of the 40‐S resulted in step‐wise extraction of proteins without inactivation of the subunits, whereas extraction with salt of a small amount of proteins from the 60‐S subunits completely inactivated them.Study of thermal inactivation showed that 40‐S had a significantly higher heat stability than 60‐S subunits.
Ribosomal Subunits from Rat Liver
Authors: Reboud Anne‐Marie , Buisson Monique , Reboud Jean‐Paul 
Published: March 2005

Large subunits from rat liver ribosomes, dialyzed against monovalent cation‐free buffer, were completely inactive in polyphenlyalanine synthesis and failed to reassociate with standard 40‐S subunits. Small subunits dialyzed under exactly the same conditions kept about 2/3 of their‐activity in poly(U)‐directed [14C]phenylalanyl‐tRNA binding or protein synthesis and could reassociate with standard 60‐S subunits. The nature of the monovalent cation present in low concentrations in the dialysis buffer was important in determining the activity of the 60‐S, but not of the 40‐S subunits: K+, Rb+ and NH+4 were more effective while Cs+, Li+ and Na+ were less effective.The various monovalent cations could be used at higher concentrations to prepare active subunits, except for Cs+ and Li+ which selectively inactivated the 60‐S subunits while modifying their conformation.Experiments with bivalent cations also showed the cationic content of the medium to be more critical for maintaining the functional form of 60‐S than of 40‐S subunits.
A General Strategy for Parameter Estimation from Isosteric and Allosteric‐Kinetic Data and Binding Measurements
Authors: Reich Jens Georg , Wangermann Gert , Falck Margrit , Rohde Klaus 
Published: March 2005

A strategy suitable for computer programming is presented which permits the estimation of kinetic parameters and of their range of statistical variation from initial‐rate measurements or from binding data. It can be used for steady‐state rate equations, rapid‐equilibrium mechanisms, binding kinetics, descriptive models such as Adair's or Hill's equations, and for the study of more complicated allosteric models. The desired kinetic equation is addressed from a model catalogue.The strategy consists of four main steps: (1) formulation of a goodness‐of‐fit criterion using the concept of the distance between observed and predicted behaviour of the model, avoiding assumptions about the statistical structure; (2) localization of the best fit, i.e. of the parameter point of minimum distance from the data by a search algorithm derived from Marquardt's method; (3) exclusion of discrepancies between model and data by testing the randomness of the vector of residual deviations and the structure of the information matrix; (4) exploration of the parameter variability based on a linear approximation of the fit criterion.Input to the programme are ligand concentrations and measured‐response data, a code number of the desired model, and a guessed starting point of the parameters which, in contrast to older methods, need not be precise. The output is either a set of parameter values with a respective region of variation, supplemented by tables and graphs of the fit obtained, or the rejection of the data with comments on the reason of failure. The possible reasons include statistical fluctuation or systematic trends in the data, lack of required information (poor experimental design), and inappropriate model (non‐unique or inconsistent kinetic model).Tests on isosteric and allosteric kinetic data lead to the conclusion that the convergence of the strategy is very good when the fit surface is well defined (good data and correct model).
Single‐Chain Structure of Human Ceruloplasmin
Authors: Rydén Lars 
Published: March 2005

In many reports human ceruloplasmin has been shown to contain several polypeptide chains. Their molecular weights have been estimated to 17000 and 59000. These findings formed the basis for proposed models of ceruloplasmin quarternary structure. Recently it was however observed, that the low molecular weight peptide chains found in commercial samples of human ceruloplasmin are absent if the protein is prepared directly from fresh serum, and evidence was presented that the earlier observed subunits were the result of limited proteolysis.The subunit structure of human ceruloplasmin has now been reconsidered using the new preparation. The reduced and cyanoethylated protein has been studied in solutions of 6 M guanidine hydrochloride. Its intrinsic viscosity and sedimentation coefficient, as well as data from gel filtration on calibrated columns of agarose gels are consistent with the presence of a single continuous polypeptide chain of about 1050 amino acid residues with a molecular weight around 120000. Together with the carbohydrate this accounts for the molecular weight of the native protein as determined by sedimentation equilibrium.
The Self‐Association of Rabbit‐Muscle Phosphofructokinase
Authors: Leonard Kevin R. , Walker Ian O. 
Published: March 2005

The sedimentation pattern of phosphofructokinase indicates that the enzyme undergoes a self‐association reaction. Alkaline pH and high ionic strength prevented the reaction. At pH 10.5 fructose 1, 6‐bisphosphate stabilised the “monomer” of the self‐association, which had s020,w= 11.9 ± 0.4 S, and D020,w= 3.22 ± 0.33 × 10−7 cm/sec giving a molecular weight of 340000. Sedimentation equilibrium gave a molecular weight of 330000 ± 12000.
The Z‐average molecular weight, measured at pH 8 by sedimentation equilibrium, increased in a sigmoid fashion with concentration from 340000 at 0.5 mg/ml to 2000000 at 7 mg/ml. By comparing the experimental curve for the variation of molecular weight versus concentration with calculated curves for open and closed polymerisations, it is suggested that the monomer associates to give a closed hexamer probably via an intermediate dimer or trimer which is present in very small amounts. The apparent association constant at pH 8.0 and 20°C was 6 × 1023 M−1 for the monomer‐hexamer reaction.
The minimum molecular weight obtained in 6 M guanidine hydrochloride, 0.1 M 2‐mercaptoethanol was 85000 ± 10000 measured by a sedimentation velocity method and 76000 ± 5000 measured by sedimentation equilibrium. This implies that the “monomer” is composed of four polypeptide chains of approximately equal molecular weight.
Kinetic Properties of a Soluble Catechol O‐Methyltransferase of Human Liver
Authors: Ball Peter , Knuppen Rudolf , Haupt Margitta , Breuer Heinz 
Published: March 2005

When 2‐hydroxyoestradiol‐17β was incubated in the presence of S‐adenosylmethionine with a 380‐fold purified catechol O‐methyltransferase from human liver, 2‐methoxyoestradiol‐17β and 2‐hydroxyoestradiol‐17β 3‐methyl ether were identified as the only metabolites. No dimethylation, transmethylation or demethylation was observed.The purified enzyme was active only in the presence of cysteine and divalent cations; magnesium was found to be the most effective cation. The temperature optimum for the methylation of 2‐hydroxyoestradiol‐17β was 42°C; the activation energy amounted to 20.9 kcal/mol. The enzyme activity had two pH optima; the pH optimum between 6.8 and 8.4 was due to maximal formation of 2‐methoxyoestradiol‐17β, whereas the pH optimum at 9.2 was due to the formation of both the 2‐ and 3‐monomethyl ether.The formation of the two isomeric monomethyl ethers increased to a maximum at a substrate concentration of 50 μM (Km value 14 μM) and then decreased with an inflection point between 75 and 100 μM (K1 value under standard assay conditions 95 μM). Whereas both monomethyl ethers were formed at the same rate up to 50 μM substrate concentration, the decrease of formation of 2‐hydroxyoestradiol‐17β 3‐methyl ether was more pronounced than that of 2‐methoxyoestradiol‐17β. Both substrate inhibition and the ratio of methylation depended on the concentrations of S‐adenosylmethionine and MgCl2. Product inhibition was also demonstrated with K1 values of 24 μM for 2‐methoxyoestradiol‐17β, 80 μM for 2‐hydroxyoestradiol‐17β 3‐methyl ether and 39 μM for S‐adenosylhomocysteine. In contrast, increasing amounts of S‐adenosylmethionine did not produce inhibition or changes of the ratio of methylation (Km value 8.5 μM).
The Reversible Inactivation of Rat‐Liver Arginase at Low pH
Authors: Hosoyama Yoshiyuki 
Published: March 2005

Rat liver arginase (l‐arginine amidinohydrolase) is inactivated by treatment with acid at 0 °C.
The inactivated or denatured enzyme can readily have its catalytic activity restored by incubation at 37 °C in neutral buffer. The amount of reactivation that occurrs depends on the Mn2+ ion concentration in the renaturation medium. The rate of renaturation also depends on Mn2.
Disc gel electrophoresis shows that dissociation into subunits occurrs by acid denaturation, the subunits having molecular weights of about 64000 and 32000, at pH 4, and 2 respectively.
The renaturation process is temperature dependent and shows first‐order kinetics. ΔH and ΔS for renaturation are 6.0 kcal/mol and – 29.8 cal/K, respectively, at 37 °C.
Some annealing process is important for renaturation and it may be a rate‐limiting process which makes the renaturation process an apparently first‐order reaction.
The renatured enzyme has the same optimum pH and Km as the native enzyme but loses its original activity in the neutral pH region.
Comparative Electron‐Microscope Studies on the Collagens Extracted from Cartilage, Bone, and Skin
Authors: Stark Marlies , Miller Edward J. , Kühn Klaus 
Published: March 2005

Long spacing segment crystallites, prepared from soluble chick bone and skin collagen with the chain composition [α1(I)]2α2 and soluble chick cartilage collagen with a chain composition [α1(II)]3, were compared in electron microscope studies after staining with phosphotungstic acid and uranyl acetate. Although comparison of bone and skin collagen long‐spacing segment preparations with similar preparations of cartilage collagen revealed several differences in intensities of cross‐striation bands, no differences in the positions of the cross‐striation bands could be observed in the three preparations, indicating that the distribution of polar and apolar regions along the cartilage collagen molecule is markedly similar to that of molecules derived from bone and skin collagen.Comparison of segment long‐spacing crystallites prepared from the various collagens also showed that the cartilage collagen is longer than the bone or skin collagen molecule by about 10–12 nm. The additional length of the cartilage collagen molecule is clearly discerned as an extra band located in the COOH‐terminal region, and is removed by treatment of the collagen with pepsin prior to precipitation as segment long‐spacing crystallites, indicating that this region contains one or more sequences in which the collagen helix cannot form.In studies on fibrils formed by the three collagen preparations, it was noted that bone and skin collagen could be readily precipitated as broad, well‐structured fibrils in which a banding pattern characteristic of native type fibrils could be easily observed. On the other hand, cartilage collagen, precipitated under identical conditions, formed slightly smaller fibrils in which a banding pattern commonly associated with native type collagen fibrils was only faintly visible in certain segments of the fibrils. These results suggest that the relatively large number of bulky carbohydrate prosthetic groups covalently attached to hydroxylysine residues in the α1(II) chains of cartilage collagen sterically hinder the deposition of staining materials and thus prevent the clear manifestation of the banding pattern in fibrils of cartilage collagen.
N6‐Monobutyryladenosine 3′ : 5′‐Monophosphate as the Biologically Active Derivative of Dibutyryladenosine 3′ : 5′‐Monophosphate in HeLa S3 Cells
Authors: Kaukel Eckhard , Mundhenk Klaus , Hilz Helmuth 
Published: March 2005

N
6,O2′‐dibutyryl cyclic AMP and O2′‐monobutyryl cyclic AMP had practically no affinity to Gilman's cyclic‐AMP‐binding kinase from muscle, while the N6‐monobutyryl derivative was bound to the protein to nearly the same degree as cyclic AMP.
N
6‐monobutyryl cyclic AMP was the only cyclic nucleotide accumulating inside HeLa cells when cultures were incubated with N6,O2′‐dibutyryl cyclic AMP. N6‐monobutyryl cyclic AMP was also accumulated when cell homogenates acted on N6,O2′‐dibutyryl cyclic AMP, while cyclic AMP and O2′‐monobutyryl cyclic AMP were rapidly degraded.
The results indicate that N6‐monobutyryl cyclic AMP is the true intracellular imitator of cyclic AMP when N6,O2′‐dibutyryl cylic AMP is added to tissues.