bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolation and Characterization of Thaumatin I and II, the Sweet‐Tasting Proteins from Thaumatococcus daniellii Benth
Authors: van der Wel Henrik , Loeve Kees 
Published: March 2005

From an aqueous extract of the fruit of the tropical plant Thaumatococcus daniellii Benth, two sweet‐tasting basic proteins, here named thaumatin I and thaumatin II, were isolated by ultrafiltration, gel nitration on Sephadex G‐50 and ion‐exchange chromatography on SE‐Sephadex C‐25, using a sodium chloride concentration gradient.The proteinaceous character of the two sweet‐tasting compounds was proven by the characteristic ultraviolet absorption spectrum, the presence of almost 100% polypeptide material as determined by the biuret method, the yield of 100% amino acids on hydrolysis with hydrochlorid acid, the positive reaction with amido black colouring agent (as used in the analysis of the fractions by polyacrylamide gel and starch gel electrophoresis) and by the disappearance of the sweet taste of the compounds after incubation with trypsin.The basic character of the two proteins appears from their isoelectric points of almost 12, as estimated by starch gel electrophoresis at different pH values, and from the precipitation of the proteins at pH 12.The molecules of thaumatin I and II are very similar as shown from their amino acid compositions, which are practically equal; they also have the same N‐terminal amino acid alanine and molecular weights of 21000 ± 600 and 20400 ± 600, respectively (calculated from ultracentrifugal data).The proteins lose their sweetness on heating, on splitting of the disulphide bridges in the molecule and at pH values below 2.5.Thaumatin I and II have an intensely sweet taste, the degree of sweetness being about 1600 times higher than that of sucrose on a Weight basis or 105 times on a molar basis. The threshold values are near 10−4% or 48 nM.
Conformational Isomers of Nitrosyl‐haemoglobin
Authors: Trittelvitz Eberhard , Sick Hinrieh , Gersonde Klaus 
Published: March 2005

The electron spin resonance spectra of the nitric oxide derivatives of horse and human haemoglobin indicate the existence of two Conformational states, the distribution of which depends on pH. The pK‐value of this allosteric transformation is 5.35. This pK is shifted by 0.3 units to 5.65 in the presence of a 50‐fold molar excess of 2,3‐bisphosphoglycerate. The ESR spectrum of nitrosyl‐myoglobin corresponds exactly to that of the alkaline species of nitrosyl‐haemoglobin, but no pH dependent change was observed. These findings might suggest a relation between the observed Conformational transition and the acid Bohr effect.At 77 K the spectrum of the acid as well as that of the alkaline species of NO‐haemoglobin indicates rhombic symmetry of the inner molecular electric field. Raising the temperature to 298 K the ESR spectrum of the alkaline species shows a transition to axial symmetry. The spectrum of the acid species exhibits hyperfine structures in the direction of the x‐ and z‐axis, that of the alkaline species in the direction of the z‐axis only. Substitution of 14NO by 15NO reveals that these hyperfine lines are caused by an interaction of the unpaired electron with the N‐nucleus of the 6th ligand. The hyperfine coupling tensor of the acid species (15N: ΔH3, 3= 23 G; 14 N: ΔH3,3,3= 17 G) is smaller than in case of the alkaline species (15N:Δ H3,3= 32 G; 14N:ΔH3,3,3= 23 G).
Investigation of the Active Center of Porcine‐Pancreatic Amylase
Authors: Elödi Pal , Móra Susan , Krysteva Milka 
Published: March 2005

The effect of maltose was studied in porcine pancreatic amylase. At neutral pH 1% (29 mM) maltose produced with amylase a difference spectrum characteristic of the perturbation of tryptophan. The molar absorption difference at the maximum wavelength was Δ290= 1200.
The difference spectrum appeared to be specific for maltose. Perturbation difference spectra measurements in 20% polyethylene glycol indicated that one tryptophyl side chain per mol amylase was involved in the interaction with maltose.
The dissociation constant of the amylase · maltose complex calculated from the concentration dependence of the absorption difference at 290 nm was Ks= 13 mM. Maltose inhibited amylase activity competitively and an inhibition constant of Ki= 25 mM was obtained, a similar value to that found spectrophotometrically. It is assumed that the tryptophyl side chain interacting with maltose may be involved in the binding of substrate by pancreatic amylase.
Metabolism of Insulin and Glucagon
Authors: Ansorge Siegfried , BOHLEY Peter , Kirschke Heidrun , LANGNER Jürgen , Wiederanders Bernd , HANSON Horst 
Published: March 2005

An enzyme catalyzing the reductive breakdown of insulin was isolated and purified from microsomes of rat liver. Its properties resemble strongly those of glutathione‐insulin transhydrogenase (thiol‐protein disulfide oxidoreductase) from bovine liver, human liver, bovine pancreas, and human kidney.The enzyme was separated from microsomes by deoxycholate and purified by gel filtration on Sephadex G‐75 and subsequent chromatography on DEAE‐Sephadex A‐50.Disc electrophoreses showed that highly purified, fresh enzyme preparations consist of only two enzymatically active proteins, forming one main band and a faint band, without any further visible contaminants.The content of glutathione‐insulin transhydrogenase in rat liver amounts to about 0.5–1% of total liver proteins as calculated from the purification factor.The molecular weight of the microsomal transhydrogenase determined by gel filtration on Sephadex G‐75 is 50000 to 55000. Using disc electrophoresis in dodecylsulfate‐containing gels molecular weights of 60000 and 121000 were determined for the main component and the second, slower‐migrating band of the enzyme, respectively.The Michaelis‐Menten constants for insulin and glutathione (in the presence of EDTA) are 31 μM (mol. wt 6000) and 1.43 mM, respectively. Maximum breakdown of 125I‐labelled insulin was found at pH 7.3.It seems very probable that our transhydrogenase from rat liver microsomes is identical or very similar to the enzyme catalyzing the reactivation of “randomly‐oxidized” ribonuclease (Anfinsen).
The Primary Structure of the Major Parvalbumin from Hake Muscle
Authors: Capony Jean‐Paul , PECHÉRE Jean‐François 
Published: March 2005

With the aim of establishing a starting point for the determination of the complete amino acid sequence of the major parvalbumin from hake muscle, the peptides resulting from the tryptic digestion of the S‐sulfo‐derivative and of the performic‐acid‐oxidized protein were examined.A total of 20 peptides were thus obtained in sufficient quantity and in a state of purity adequate for further studies. Their complete or partial sequence is reported.When due account is taken of obvious overlaps, the total of these peptides fully accounts for the composition of the whole molecule with the exception of one alanine residue, and for the number of peptides expected from the presence of 12 lysines and 1 arginine in this parvalbumin.
A New Class of Heptose‐Defective Mutant of Salmonella typhimurium
Authors: Lehmann Volker , HÄMMERLING Günter , Nurminen Marjatta , MINNER Inge , Ruschmann Ellen , LÜDERITZ Otto , Kuo Tseng‐Tong , STOCKER Bruce A. D. 
Published: March 2005

Salmonella typhimurium rfa‐657 strains, including both mutants and transductants, were shown to contain in their lipopolysaccharides both the (usual) l and the d‐isomer of glycero‐d‐manno‐heptose. By the application, in sequence, of two different extraction procedures S and R form lipopolysaccharides could be isolated separately from a representative rfa‐657 strain. The R lipopolysaccharide was predominantly of the Re chemotype, only a few 2‐keto‐3‐deoxyoctonate (KDO) residues being substituted by heptose (Rd2 chemotype) or by longer core chains. The d‐heptose was enriched in the R lipopolysaccharide, while the S lipopolysaccharide contained mainly the natural l‐isomer. It was found that d‐heptose can replace l‐heptoses I to III of the wild‐type core. However, an elongation to completeness of the core stubs containing d‐heptose seldom occurs.The heterogeneity in structure of the lipopolysaccharide produced by this class of (leaky) mutants is assumed to be due to an altered 6‐epimerase which, in the wild form, catalyses the conversion of NDP‐d‐glycero‐d‐manno‐heptose into NDP‐l‐glycero‐d‐manno‐heptose and which is determined by the gene rfa‐657 situated between cysE and pyrE. The symbol rfaD is proposed for this gene.
Thermal Stability of Poly(U) · tRNA: Ribosome Complexes with Phe‐tRNAPhe and Peptidyl‐tRNAPhe
Authors: Hamburger Albert David , LAPIDOT Yehuda , de Groot Nathan 
Published: March 2005

The stability of ribosomal complexes, carrying [14C]Phe‐tRNAPhe, Gly‐Gly‐[14C]Phe‐tRNAPhe or Ac[14C]Phe‐tRNAPhe at the A site (aminoacyl site) or at the P site (peptidyl site) has been studied with thermal dissociation techniques. Gly‐Gly‐Phe‐tRNAPhe forms a more stable P‐site complex but a less stable A‐site complex than Phe‐tRNAPhe. The P‐site complex with Gry‐Gly‐Phe‐tRNAPhe is more stable than the A‐site complex with the same substrate. Phe‐tRNAPhe, bound enzymatically at the A site, forms a more stable complex than Phe‐tRNAPhe bound non‐enzymatically at the P site. The complex with Phe‐tRNAPhe, formed enzymatically in the presence of GTP, is considerably more thermostable than the complex formed in the presence of Guo‐5′‐P2‐CH2‐P.These results provide additional evidence that aminoacyl‐tRNA and N‐blocked aminoacyl‐tRNA interact with different stabilities with the ribosomal binding sites. It is suggested that the observed differences in thermal stabilities reflect the substrate specificity of the peptidyl transferase.
Dihydropteridine Reductase
Authors: Lind Kirsten E. 
Published: March 2005

Binding of NADH and quinoid dihydropteridine to dihydropteridine reductase from rat liver has been studied by the techniques of protein fluorescence quenching and ligand protection.The dissociation constans obtained for the binary complexes by the two methods were in agreement.For NADH, the constant was 0.07 μM and for quinoid dihydropteridine, 2–3 μM (30 °C, pH 6.8). The constants have been compared with the apparent Michaelis constants.
Variantes de mycosides caractérisées par des résidus glycosidiques substitués par des chaînes acyles
Authors: Gastambide‐Odier Mireille 
Published: March 2005

The hydrogenolysis of peracetylated mycoside G′ cleaves this mycoside between the aromatic nucleus and the acylated sugars. The mass spectrum of one of these sugars is typical of an ethyl 2‐O‐mycolyl‐3‐O‐methyl‐4‐O‐acetyl‐6‐deoxypyanoside (I): The highes peaks (m/e 1243, 1215 and 1187) are due to splitting on both sides of the methyl branching of the mycolic chain. Other important peaks prove that the sugar cycle is pyranic, that the mycolic chain is bound to the hydroxyl carried by C‐2 and that the methoxyl group is on C‐3. The acyl chain (IV) fragments (m/e 995, 967 and homologues) are typical of a mycolic acid with a methoxyl group (m/e 253, 281, 325) and a C22 side chain, as indicated by the +CH=6;Ċ–C22H45 peak.The structure of mycosides A, B and G comprising polar sugars bound through an aromatic nucleus to an apolar aglycone suggests that these substances might function as a carrier or cofactor in the vicinity of the bacterial membrane or close to the bacterial cell wall. That mycolic acids which esterify hydroxyl groups of mycoside sugars are found to exist favors this conclusion, the more so as mycolic substances are constituants of the cell walls (arabinogalactane mycolate) and of the bacterial outer layer (cord factor).
Metabolism of Ethanol and Fructose in the Isolated Perfused Pig Liver
Authors: Damgaard Stig E. , Lundquist Frank , Sestoft Leif , Tønnesen Klavs , Hansen Finn Vallø 
Published: March 2005

Ethanol at concentrations below 10 mM was oxidized at a rate of 0.7 μmol×g−1× min−lby the perfused pig liver. Infusion of fructose caused a stimulation (up to 120%) of ethanol oxidation, which was proportional to the rate of fructose elimination.Stimulation was observed also whend‐glyceraldehyde (a fructose metabolite) was used. Even at highd‐glyceraldehyde concentrations, the increase in ethanol metabolism was less than with fructose.Hepatic acetate metabolism was not affected by ethanol but was stimulated up to 100% by fructose in the presence of ethanol.The concentration ratios of sorbitol/fructose and lactate/pyruvate in the perfusion medium were increased in experimental periods with ethanol and fructose compared to periods with fructose alone. The data indicate equilibrium between these metabolites and the free NADH/NAD in the cytosol.The steady‐state concentrations of D‐glyceraldehyde and glycerol were increased when ethanol was infused together with fructose, while the production ofd‐glycerate was reduced to zero.The rate of fructose elimination was not influenced by ethanol, although the output of lactate and glucose were diminished.Accumulation of the reduced metabolites (sorbitol, glycerol,l‐glycerol 3‐phosphate) accounted for only a small part of the reducing equivalents generated during fructose‐stimulated ethanol oxidation. Complete oxidation of the ethanol metabolized would require 3.6 μmol O2×g−1×min−lcompared to a measured uptake of 1.8 μmol× g−l×min−1. As ketone bodies and acetaldehyde were not produced in significant amounts, the retained acetate must be used in syntheses,e.g.of fatty acids.The experimental results are interpreted in terms of a model, the malate shuttle. Data from experiments with pyrazole and dinitrophenol support the interpretation.
Introduction of “Nicks” and “Chops” into Human Mitochondrial DNA in vivo and in vitro
Authors: Koch Jürgen 
Published: March 2005

After prolonged exposure of HeLa cells (ATCC: CCL2) to ethidium bromide (1μg× ml−l in the growth medium) the bulk of the mitochondrial DNA of these cells sediments with a sedimentation coefficient of 21 S. This DNA species is a linear duplex DNA molecule with the length of the circumference of the closed circular mitochondrial DNA. This linear DNA contains single‐strand nicks or gaps as shown by sedimentation after denaturation or by sedimentation through alkaline sucrose gradients. The number of fragments obtained after denaturation increased with decreasing molecular weight reaching a peak at the fragment size of 1/10 of the single‐stranded mitochondrial DNA.Most of the covalently closed phosphodiester backbones of the supercoiled mitochondrial DNA contain three sites which are sensitive to cleavage by alkali and at least one site which is sensitive to the action of RNAase.
Nucleophilic Competition in Some β‐Galactosidase‐Catalyzed Reactions
Authors: Viratelle Odile M. , Yon Jeannine M. 
Published: March 2005

A study of nucleophilic competition in β‐galactosidase‐catalyzed reactions has been performed with different substrates: o, m and p‐nitrophenyl β‐d‐galactosides, phenyl β‐d‐galactoside, o‐aminophenyl, β‐d‐galactoside, p‐aminophenyl, β‐d‐galactoside, o‐nitrophenyl α‐l‐arabinoside. For each substrate the limiting step and the individual rate constants have been determined. The rate of formation of the galactosyl‐enzyme intermediate, k2, does not correlate with the Hammett values, suggesting that this step remains more complex than a single chemical reaction.A preliminary investigation of the effect of pH and Mg2+ concentration on each individual rate constant is presented. Both k2 and k3 seem to exhibit the same pH profile.The action of various nucleophilic compounds on the galactosyl‐enzyme has been tested. A peculiar effect of 2‐mercaptoethanol has to be emphasized; the behaviour of this nucleophile has been analyzed and discussed.
The Effects of Ionic Strength on Termination of Transcription of DNAs from Bacteriophages T4, T5 and T7 by DNA‐Dependent RNA Polymerase from Escherichia coli, and the Nature of Termination by Factor ρ
Authors: Schäfer Rolf , Zillig Wolfram 
Published: March 2005

Ionic strength influences (a) the equilibrium between the monomeric and the dimeric form of DNA‐dependent RNA polymerase from Escherichia coli, in the free state, (b) the primary binding of the enzyme to sites on the template, (c) the velocity of a state transition involved in initiation and (d) termination (or block) of transcription.On T7‐ and T5‐DNA transcription is terminated, with release of the transcript, at both high and low ionic strength at the same sites but the enzyme is released only at high ionic strength allowing reinitiation whereas at low salt concentration the complex of enzyme with terminator and σ does not dissociate.On T4‐DNA transcription at low ionic strength is arrested at a class of low‐ionic‐strength blocking sites without release of the transcript.In the presence of “termination factor”ϱ and ϰ at low ionic strength transcription of T4, T5 and T7‐DNA is arrested at another class of blocking sites again without release of the transcript. The average relative positions of the three different types of blocking sites between the initiation site and the terminator have been determined for T4‐DNA.Implications of these results are discussed.
Some Reactions of Insulin at Non‐Polar Surfaces
Authors: Browne Marjorie , Cecil Rupert , Miller Janet C. 
Published: March 2005

The behaviour of insulin at decane/water interfaces has been studied under a variety of conditions. A state of equilibrium has been shown to exist between insulin in solution and on the interface which appears to be independent of concentration. It is changed when a charge is introduced at the interface.Dansyl chloride was added to the decane so as to label that part of the insulin molecule in contact with the interface. Reaction was confined to the B1 phenylalanine and evidence is given which shows that insulin adsorbed on the interface is dimeric. Two products were found with one and two dansyl groups respectively per dimer. The former is 50% active and the latter inactive by the mouse convulsion method. This is explained by assuming that the monomer is the active species.Surface tension experiments were carried out to determine the area of the insulin dimer at the interface. The results obtained are consistent with the X‐ray data.
Messenger Ribonucleoprotein and Initiation Factors in Rabbit‐Reticulocyte Polyribosomes
Authors: Nudel Uri , Lebleu Bernard , Revel Michel , Zehavi‐Willner Tova 
Published: March 2005

EDTA dissociation of reticulocyte polyribosomes liberates globin mRNA as a nucleoprotein. An attempt to compare the proteins forming the mRNA · protein complexes with the initiation factors of protein synthesis is presented here.Two conditions are described under which initiation factors are removed from hemoglobin‐synthesizing ribosomes. One is after treating the polyribosomes with a high salt concentration; the other is by isolating ribosomes from reticulocytes at an advanced state of maturation which have lost their initiation factors. In both cases it is shown that the mRNA remains associated with the ribosomes and with the proteins forming the mRNA · protein.Moreover both mRNA and mRNA · protein are translatable in a heterologous cell‐free system and their translation is stimulated to the same extent by the addition of reticulocyte initiation factors.Initiation factors are therefore different physically and functionally from the proteins of the mRNA · protein.
A Study of the Interactions between Monomeric Tropocollagen and Glycosaminoglycans
Authors: ÖBrink Björn 
Published: March 2005

Monomeric, lathyritic tropocollagen and a variety of well‐characterized glycosaminoglycans have been used in a light‐scattering study of the interaction that occurs between these macro‐molecules under physiological ionic conditions. Additional information has been obtained by turbidimetric and precipitation studies. A binding to collagen of chondroitin 4‐sulphates, derma‐tan sulphates, heparan sulphates, heparin and proteoglycans of chondroitin sulphate and dermatan sulphate was observed. The complex formation was electrostatic in nature and was abolished with increasing ionic strength.Keratan sulphate did not bind to collagen, indicating either that uronic acid was a prerequisite for the interaction or that a charge density of more than one negative charge per disaccharide was required. Polysaccharides which contained l‐iduronic acid showed a stronger interaction than polysaccharides containing only d‐glucuronic acid. As a general rule the interaction seemed to increase with increasing chain length of the polysaccharide and increasing charge density.The results of studies on mixtures of tropocollagen and proteoglycans indicated that the properties of the polysaccharide chains per se were of importance for the mode of reaction between the proteoglycans and collagen.Hyaluronic acid was not to any significant extent bound to collagen. This polysaccharide and tropocollagen affected each other by a mutual steric exclusion with a concomitant increase in the activity of the tropocollagen molecules.
Differences in Nucleotide Sequences of Ribosomal RNA between the Liver and a Hepatoma of C3H/He Mice
Authors: Hashimoto Shuichi , Muramatsu Masami 
Published: March 2005

Highly purified ribosomal 18‐S and 28S RNA have been prepared from the liver and the hepatoma (MH 134) of C3H/He mice labeled with 32P and subjected to pancreatic RNAase digestion. Analysis of oligonucleotide patterns with two‐dimensional electrophoresis indicated that there were slight but significant differences between the liver and the hepatoma both for 18‐S and 28‐S RNA. Remarkable was the fact that a tetranucleotide sequence, Y‐(G, G*)‐Cp where G* represents a modified G and Y, an unspecified pyrimidine nucleotide, and a hexanucleotide sequence, Y‐A‐A‐A‐A‐Up that were found in the 18‐S RNA of normal liver were always missing in the 18‐S RNA of the hepatoma.Evidence was also obtained that both 18‐S and 28‐S RNA of these cells are not entirely homogeneous but consist of molecules with some heterogeneity with respect to nucleotide sequences.These results were discussed under the concept of differential transcription of redundant and heterogeneous ribosomal genes in mammalian cells.