bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light Absorption of Flavosemiquinone Metal Chelates
Authors: Müller F. , Hemmerich P. , Ehrenberg A. 
Published: March 2005

The light absorption of flavosemiquinone metal chelates (Zn2+, Cd2+, Mn2+, Co2+, Ni2+, Fe2+, Mo5+, and Cu+) in aprotic polar solvents has been studied. The light absorption of flavosemiquinone metal chelates, the uncomplexed cation and anion free radicals, and the corresponding, very unstable, flavoquinone metal chelates are compared. The visible spectra of the flavosemiquinone metal chelates, irrespective of the metal, are very similar to that of the free radical anion. In addition, they show a rather unique, sharp transition in the near infrared range (650 to 850 nm). The extinction coefficients for d1, d5, d6, d7, d8, and d10 metal centres are between 10 and 2 × 103 M−1cm−1. Solvents that act as quaternary ligands (pyridine, acetonitrile, but not 2,6‐lutidine) strongly affect this near infrared transition, but not the visible spectrum. We therefore conclude that the near infrared absorption reflects the symmetry of the flavosemiquinone‐metal‐H2O‐solvent complex.The molar extinction coeffcients in the near infrared are independent of chelate concentration, solvent polarity, and ionic strength, and the optical densites are proportional to total spin concentration as monitored by electron spin resonance (for systems of total spin 1/2, i. e. with d10 central ions). This excludes association phenomena. Altering the flavin moiety, even slightly, effects the light absorption spectrum in the visible and near infrared regions.This near infrared absorption may be a useful tool for detecting flavin‐metal chelation in enzyme systems.
The Interaction of α‐Actinin with F‐Actin and its Abolition by Tropomyosin
Authors: Drabikowski W. , Nowak E. 
Published: March 2005

The interaction of α‐actinin with F‐actin was examined with the use of the viscometric technique under various conditions.
α‐Actinin causes the gelation of F‐actin when added both before and after polymerization.
The interaction of α‐actinin with F‐actin seems to be much stronger at 0° than at 21°. In the latter case it takes place only when actin is polymerized with 0.1 M KCl, but not with 1 mM MgCl2 or CaCl2.
Tropomyosin, when added before α‐actinin, prevents the formation of F‐actin gel, and when added to already formed gel, causes its disappearance.This abolishing effect of tropomyosin is much stronger at 21° than at 0°.
The results are discussed in view of the possible competition between tropomyosin and α‐actinin for the binding to F‐actin.
Mechanism of Thyroxine Formation from Diiodotyrosine and p‐Hydroxydiiodophenylpyruvic Acid
Authors: Blasi F. , Fragomele F. , Covelli I. 
Published: March 2005

The mechanisms of the non‐enzymic synthesis of thyroxine from diiodotyrosine and its keto acid derivative 4‐hydroxy‐3,5‐diiodophenylpyruvic acid has been investigated.
The time course of the overall coupling process has been studied by following the formation of thyroxine and the disappearance of the reactants from the incubation medium. Thyroxine formation has a lag phase during which diiodotyrosine remains unchanged, whereas 4‐hydroxy‐3,5‐diiodophenylpyruvic acid disappears very rapidly.
Disappearance of 4‐hydroxy‐3,5‐diiodophenylpyruvic acid from the reaction mixture is due to the formation, besides of a degradation product, of an oxidized form of the keto acid which reacts with diiodotyrosine without a lag phase even in the absence of oxygen. This oxidized intermediate is formed by the uptake of 2 atoms of oxygen per mole of the keto acid. Its spectrum in the ultraviolet region is very similar to that of the unmodified keto acid; furthermore it is stabilized by borate ions and is able to oxidize iodide. The most likely structure of the oxidized intermediate of the 4‐hydroxy‐3,5‐diiodophenylpyruvic acid, therefore, is that of a peroxide.
Propylgallate, a radical scavenger known to block free radicals originated from 4‐hydroxy‐3,5‐diiodophenylpyruvic acid, increases the lag phase, inhibits the oxygen uptake 4‐hydroxy‐3,5‐diiodophenylpyruvic acid and decreases the overall yield of thyroxine if added during the lag phase; it is uneffective when added during the anaerobic period of the coupling reaction.
The following mechanism can be envisaged: (a) in a first step 4‐hydroxy‐3,5‐diiodophenyl‐pyruvic acid looses an electron thus originating a free radical; (b) in a second step 2 atoms of oxygen are taken up by the free radical and a peroxide‐like derivative is formed; (c) in the third step, not requiring the presence of oxygen, the peroxide derivative of the keto acid instantly couples with diiodotyrosine to form thyroxine.
Korrelation des unspezifisch permeablen mitochondrialen Raumes mit dem „Intermembran‐Raum”
Authors: Pfaff E. , Klingenberg M. , Ritt E. , Vogell W. 
Published: March 2005

The term “unspecific permeability” in mitochondria is defined for describing a rapid equilibration of solutes between the extraamitochondrial space and a portion of the intramitochondrial space. It appears to be a property of the outer membrane and is restricted only by the size of the molecule (maximal molecular weight of 5,000–12,000).The unspecifically permeable space varies considerably. It ranges from 20–80% in different preparations of mitochondria. For a single mitochondrial preparation it is shown to be of equal volume for various small molecules such as sucrose, adenine nucleotides, NAD+and aspartate.The total aqueous phase of rat liver mitochondria in isotonic sucrose medium ranges from 2.5–3.4 μl/mg protein; the aqueous part of the impermeable space from 0.8–1.8 μl/mg protein. Only about 1 μl of this portion expands osmotically and represents the solvent for endogenous mitochondrial solutes. The major part (about 0.4–0.6 μl/mg protein) of the residual water of the impermeable space may be attributed to the hydrate shell of mitochondrial protein.The unspecifically permeable and the impermeable space of the mitochondria are compared with the morphologically defined intermembrane and matrix space. The tonicity of the incubation medium was varied over a large range for rat liver and rat kidney mitochondria in order to facilitate this comparison. Large variations in the ratio of sucrose permeable to impermeable space (ranging from 1:3 in liver mitochondria to 3:1 in kidney mitochondria) correspond to changes in the ratio of the areas covered by the intermembrane and matrix space in the sections seen in the electron‐micrographs. Mitochondria with low unspecific permeability are homogenous, mitochondria with high unspecific permeability show greater individual variability at all tonicities.
Isolation and Properties of a Mouse Serum Prealbumin Excreted in Urine
Authors: Reuter A. M. , Hamoir G. , Marchand R. , Kennes F. 
Published: March 2005

A method is described for the isolation of the fastest prealbumin fraction PA1 from mouse serum.This fraction appears to behave identically to the urinary prealbumin fraction in electrophoretic migration, strain and sex dependency and in immunological reactions.Molecular weight is determined by diffusion and sedimentation as well as by sedimentation‐diffusion equilibrium.The apparent lower molecular weight of serum prealbumin is due to its contamination by polysaccharides extracted from starch gel in the course of its isolation.
Study of the Groups Controlling the Activity and Conformation of Chymotrypsin at Alkaline pH: N‐Terminal Isoleucine and Tyrosines
Authors: Karibian D. , Laurent C. , Labouesse J. , Labouesse B. 
Published: March 2005

It is shown that the change in activity and structure of acetyl‐δ‐chymotrypsin in the pH 7–11 range is not correlated with the ionizations of tyrosine residues.The pKs of the two titratable tyrosines of acetyl‐δ‐chymotrypsin are found to be 10.2 and 11.5, at 15° (9.6 and 10.8 after correction for electrostatic interactions), and those of the starting acetylated zymogen are 10.5 and 12.1 (10.0 and 11.5 after identical corrections). The plot of log rate of deacetylation of the titratable tyrosines versus pH is linear between pH 9 and pH 12. At a given pH there is a linear relation between the log deacetylation rate and the pKs of the residues. The pH rate profile of acylation of acetyl‐δ‐chymotrypsin by 4‐carboxy‐3‐nitrophenyl‐N,N‐diphenylcarbamate is bell‐shaped, with a maximum at pH 7.9 at 15°, in 0.14 M KCl. The right side of the curve shows a pKapp of 8.9, whether the exposed titrable tyrosines of the enzyme are acetylated or not. A similar pKapp (9.1) is found for the pH‐dependent change in optical rotation of the acetylated enzyme, when the exposed tyrosines are acetylated. After correction for electrostatic interactions, this apparent pK becomes 8.4 and can be assigned only to the α‐aminogroup of the N‐terminal isoleucine.
Induction and Repression of Mitochondrial ATPase in Yeast
Authors: Somlo M. 
Published: March 2005

A simple mechanical procedure for the preparation of particle‐bound Mg‐ATPase is described. It represented at least 80% of total ATPase activity, both in the case of aerobically and of anaerobically grown yeast. When analyzed in a sucrose gradient, ATPase from aerobic yeast sedimented with NADH‐oxidase. ATPase from aerobic or anaerobic yeast showed 2 pH optima, as had been described for ATPase localized in carefully prepared and purified yeast mitochondria. Particle‐bound ATPase from aerobic or anaerobic yeast showed pronounced oligomycin sensitivity.
Anaerobically grown yeast synthesized particle‐bound Mg‐ATPase at the low basal rate of 7–10 μmoles P/10 min/mg protein. During O2‐induction without growth, respiratory enzymes and ATPase were induced simultaneously. Both inductions were inhibited by acti‐dione.
Aerobically grown, glucose‐repressed yeast synthesized ATPase at a rate similar to anaerobic yeast. Progressive derepression during growth produced a simultaneous increase of the rate of cell respiration (30–270) and of ATPase activity (10–60).
Ethanol‐grown cells had a constant high Qo2 and synthesized ATPase at the high constant rate of 60.
Regulation of ATPase synthesis was strictly identical when activity was measured at the two pH optima, suggesting the presence of a single mitochondrial ATPase. The possibility of separate phosphorylating and hydrolytic sites on the enzyme is discussed.
Regulation of the Enzymes of the β‐Ketoadipate Pathway in Moraxella calcoacetica
Authors: Cánovas J. L. , Johnson B. F. , Wheelis M. L. 
Published: March 2005

Further evidence for coordinacy of enzymes operative in the protocatechuate branch of the β‐ketoadipate pathway in Moraxella calcoacetica has been obtained through studies with an analog of protocatechuate, 3‐hydroxy‐4‐methylbenzoate. This compound, which is not metabolizable by M. calcoacetica, inhibits the induced synthesis of shikimate dehydrogenase, protocatechuate oxygenase, carboxymuconate lactonizing enzyme, carboxymuconolactone decarboxylase, β‐ketoadipate enol‐lactone hydrolase I and β‐ketoadipate succinyl‐CoA transferase I, by the wild type. It also effectively abolishes constitutive synthesis of these enzymes by mutants with impaired protocatechuate oxygenase function.Mutants in which the regulatory control of these enzymes is modified have been isolated. Such mutants are still inducible, but are very poorly induced by protocatechuate, the metabolite which is the normal inducer of these enzymes in the wild type. However, 3‐hydroxy‐4‐methylbenzoate, which interferes with induction in the wild type, has become an effective inducer for the mutants.
Excess of α‐Globin Synthesis in Homozygous β‐Thalassemia and its Removal from the Red Blood Cell Cytoplasm
Authors: Bargellesi A. , Pontremoli S. , Menini C. , Conconi F. 
Published: March 2005

The intracellular behaviour of the excess newly synthesized α‐globin has been studied by incubating peripheral blood and bone marrow samples from 9 homozygous β‐thalassemic subjects with labeled amino acids. The globin chains present in the cytoplasm and in association with the stromal material have been separated by column chromatography, and the incorporation of radioactivity has been determined for each globin at various incubation times.The results obtained show that the excess of α‐globin is removed from the cell cytoplasm and becomes associated with the stromal material.
Correlation between Anion Uptake and the Movement of K+ and H+ across the Mitochondrial Membrane
Authors: Palmieri F. , Quagliariello E. 
Published: March 2005

The relationship between the H+ and K+ movement across the mitochondrial membrane and the distribution of anions between the intra‐ and extramitochondrial space has been analyzed in the presence of uncouplers, nigericin and nonactin.

Mitochondria accumulate added anions in the presence of respiratory inhibitors and oligomycin. This accumulation is accompanied by the exit of endogenous anions. Respiration or ATP hydrolysis does not, in itself, increase anion accumulation, but only in as much as it gives rise to proton ejection and cation uptake.
In sucrose medium anion uptake, found in the presence of respiratory inhibitors and oligomycin, is inhibited by uncouplers, nigericin and nonactin, all of which cause H+ uptake and K+ release. The ratio of the intra‐ to the extramitochondrial concentration of endogenous anions is also strongly diminished by uncouplers, nigericin and nonactin.
With nonactin‐pretreated mitochondria, uncouplers, even at very high concentrations, do not inhibit anion uptake.
With nonactin, as the external K+ concentration is increased, the uptake of H+ is progressively decreased and similarly the anion uptake inhibition is diminished.
The 2,4‐dinitrophenol‐induced uptake of H+ is unaffected by the presence of K+ in the medium up to a concentration of 125 mM. The inhibition of anion uptake and the efflux of endogenous anions, induced by dinitrophenol, are equal in the presence or absence of 100 mM KCl.
In the presence of an external concentration of 100 mM KCl, with nigericin the uptake of H+ is strongly diminished and similarly the anion uptake inhibition and the efflux of endogenous anions are greatly decreased. With nonactin, H+ ejection occurs accompanied by stimulation of anion uptake.
The ratio of the intra‐ to the extramitochondrial concentration of succinate increases as the external pH decreases. This increase of anion uptake by lowering the pH is inhibited by dinitrophenol.
It is concluded that inhibition of anion uptake and efflux of endogenous anions are dependent upon the uptake of H+ by the mitochondria and vice versa H+ ejection is responsible for stimulation of anion uptake.
Synthèse des messagers précoces phagiques chez Escherichia coli infecté par T4 durant une carence spécifique en aminoacide
Authors: Legault‐Démare L. , Malhié A. , Gros F. 
Published: March 2005

It has been known for many years that the rate of ribosomal and transfer RNAs synthesis in bacteria is determined by the internal amino acid concentration but the existence of the same mechanism of regulation for messenger RNA has not been clearly demonstrated yet.This work was done to determine if the amino acid regulation also governs phage early messenger RNA synthesis in T4 infected Escherichia coli cells, in which the synthesis of bacterial RNA is known to be turned off rapidly after infection.The determination of the rate of messenger synthesis in the presence and in the absence of the required amino acid was done (a) by measurement of the amount of radioactivity from labelled RNA which is hybridizable to phage DNA; (b) by estimation in each sample of the amount of messenger RNA which can compete with a messenger RNA labelled in the presence or in the absence of the required amino acid for the complementary sites of phage DNA.By direct hybridization it was found that in the absence of the required amino acid the rate of labelling of phage messenger RNA is reduced in a stringent strain, but not in a relaxed strain.By hybridization competition it was found that the molecular species of phage messenger RNA which can be synthesized in the absence of the required amino acid are present at the same concentration in infected cells either in the presence or in the absence of the amino acid.A study of the kinetics of formation of the messenger pool showed that, as early as the first minute of infection, all the molecular species of messenger are present in the same proportions in the stringent cells whether amino acid‐starved or not.It is concluded that in a stringent strain those molecular species of messenger which do not require the presence of specific viral protein for their formation are synthesized at the same rate in the presence or in the absence of a required amino acid.The implications of these results concerning the control of transcription by amino acids are discussed.
Magnetic Resonance and Kinetic Studies on the Manganese Activated Arginine Kinase Reaction
Authors: O'sullivan W. J. , Virden R. , Blethen S. 
Published: March 2005

Proton relaxation rate studies have been used to study the interaction between arginine kinase from two sources, Homarus vulgaris and Homarus americanus, and manganous ion, MnADP‐ and MnATP2‐, respectively. There was negligible interaction between Mn2+ and the H. vulgaris enzyme but a small effect with the H. americanus enzyme. In both cases, a large enhancement of the proton relaxation rate was seen on the addition of ADP or ATP to a solution containing Mn2+ and enzyme. It was concluded that the enzyme combines with MnADP− or MnATP2‐ rather than with Mn2+.Enhancements of the proton relaxation rate of the ternary complexes, MnADP‐E (45), Mn2′‐dADP‐E (28) and MnATP‐E (17), were obtained with the H. vulgaris arginine kinase and Mn3′‐dADP− and Mn2′‐dATP2‐ were also demonstrated to form ternary complexes with this enzyme. For arginine kinase from H. americanus, values for MnADP‐E (17), Mn2′‐dADP‐E (approx. 12) and MnATP‐E (approx. 8) were determined. A comparative kinetic study demonstrated reasonable agreement between the kinetically determined Km values and dissociation constants from the proton relaxation rate data. It was also found that for both enzymes, there was a correlation between the enhancement and maximum velocity values, ADP > 2′‐dADP and ATP > 2′‐dATP which could be interpreted as indicative of a graded degree of substrate induced conformational change. The proton relaxation rate and kinetic studies indicated small but probably significant differences in the properties of the two enzymes.Proton relaxation rate studies provided evidence for a second substrate induced conformational change on the addition of l‐arginine to the ternary MnADP‐enzyme complex. No significant effect was observed with d‐arginine, which is a competitive inhibitor with respect to l‐arginine.
The Role of Heme in the Regulation of δ‐Aminolevulinic Acid and Heme Synthesis in Rabbit Reticulocytes
Authors: Neuwirt J. , Poňka P. , Borová J. 
Published: March 2005

The problem of the feedback inhibitory effect of heme on its own synthesis in erythroid cells was studied using different methods.
The activity of δ‐aminolevulinic acid synthetase was determined in the insoluble particles containing mitochondria and stroma prepared from rabbit reticulocytes and in the lysate from these reticulocytes.
The effect of hemin on the incorporation of [2‐14C]glycine into heme was measured in the lysate from rabbit reticulocytes.
The effect of hemin on the incorporation of 59Fe into heme was studied in reticulocytes with artificially elevated labeled non‐heme iron pool.
All the three different methods used produced evidence that hemin does not directly inhibit its own synthesis.
No feedback control by hemin of heme synthesis in the rabbit reticulocytes at the level of δ‐aminolevulinic acid synthetase could be proved.
The principal site of inhibition by hemin in intact reticulocytes appears to be the transfer of iron into the cells.
NMR‐Studies on the Structure of the Active Site of Pancreatic Ribonuclease A
Authors: Rüterjans H. , Witzel H. 
Published: March 2005

The chemical shift of the C‐2 imidazole protons of the histidine residues of pancreatic ribo‐nuclease has been studied as a function of pH in 2H2O. Upon protonation of the imidazole ring the C‐2 proton magnetic resonance signal shifts about 1.0 ppm to a lower field. Thus titration curves and approximate pK values of the histidine residues are obtained. The pK values of histidine 119 and histidine 12 of the active site are unusually low and shift by 1.0 and 0.7 units to higher values when the NaCl concentration is changed from 0.1 M to 0.4 M, whereas the pK value of histidine 105 shifts only by about 0.2 units. This indicates the presence of a positively charged group in the immediate environment of histidine 119 and histidine 12. The abnormal chemical shift of the histidine 48 C‐2 proton at low pH is explained by means of an interaction of histidine 48 with the carboxylate anion of aspartic acid 14. From an analysis of the titration curves of histidine 119 and histidine 12 the existence of an enzyme species in which both imidazoles are connected by a hydrogen bond is derived. The C‐2 proton magnetic resonance signals of histidine 119 and histidine 12 shift to a lower field when inhibitors bind to the enzyme. Both histidines are then kept in a protonated form up to the pH range of 7–8. The apparent pK values are higher in the cytidine 2′‐phosphate‐ribonuclease complex than in the cytidine 3′‐phosphate‐ribonuclease complex. A similar shift of the histidine 119 and histidine 12 signals is observed with binding of pyrophosphate to ribonuclease indicating that only the phosphate group causes the behaviour of the histidines. Shifts of the C‐6 proton magnetic resonance signal of the pyrimidine ring indicate an additional binding of the base to an aromatic side chain of the enzyme.The mechanism for the binding process proposed in previous papers by Witzel and coworkers in which histidine 119 and lysine 41 are the binding groups of the enzyme, whereas histidine 12 takes up a proton when being released from its binding to histidine 119, is in agreement with the results reported in this communication.
Effect of Monovalent Cations on the Activity of the DNA Polymerase of Escherichia coli B
Authors: Klenow H. , Henningsen I. 
Published: March 2005

The effect of a number of inorganic salts containing monovalent cations on the activity of the DNA polymerase from E. coli B has been investigated under a variety of conditions. The following results were obtained.

In the presence of buffers prepared from organic amines and HCl the enzyme activity is stimulated 3‐ to 15‐fold by chlorides containing K+, Rb+, Cs+ or NH+4. The buffer concentration influenced the degree of stimulation and the shape of the activation curves. The activation constant for KCl decreased with increasing buffer concentration and with increasing pH. NaCl and LiCl had little or no stimulating effect. The latter two salts counteracted the stimulating effect of the four former salts.
In the absence of amine‐HCl buffers it was found that below certain concentrations sodium, potassium and lithium glycinate buffers and potassium and sodium phosphate buffers stimulated the enzyme activity. Data were obtained in favour of the possibility that the monovalent cations under these conditions are indispensible activators for the DNA polymerase reaction.
The pattern of stimulation of the enzyme activity by KCl at various amine‐HCl buffer concentrations was similar at different pH values in the pH range from 6.5 to 9.3. At pH 10.5, however, KCl stimulated at low buffer concentrations while all concentrations of this salt inhibited at higher buffer concentrations. In the presence of optimal concentrations of KCl and amine‐HCl buffers the pH optimum curve had a plateau reaching from pH 7.7 to about pH 10.5.
The stimulating effect on the enzyme activity observed for potassium salts seems not to be due to an effect on the binding of the substrates to the enzyme but rather to an effect on the catalytic activity of the enzyme.
The DNA degrading activity of the enzyme preparation was stimulated by KCl and inhibited by LiCl.