bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Necessity of an Electric Potential Difference and its Use for Photophosphorylation in Short Flash Groups
Authors: Junge Wolfgang , Rumberg Bernd , Schröder Hartmut 
Published: March 2005

The ATP‐synthesis and the electric phenomena on the thylakoid membrane have been studied under excitation of photosynthesis with short flash groups. The light induced electric potential difference has been measured by means of field indicating absorption changes around 523 nm.It is shown that upon excitation with short flash groups a certain electric potential difference is required before ATP can be synthesized. Moreover it is confirmed that the ATP‐synthesis is accompanied by an additional flux of protons down their electrochemical potential gradient. Correlation between the number of protons which have flowed across the ATPase coupled pathway, and the number of ATP‐molecules which have been formed, yields a ratio H+/ATP = 3.Since this ratio includes only those protons, which have interacted with the ATPase complex, it represents the lower limit for H+/ATP‐ratios determined by any other method.The necessity of a certain electric potential difference and the fact that 3 H+ have to be translocated down their electrochemical potential difference before one molecule of ATP can be synthesized is consistent with the chemiosmotic postulate, that the ADP ∼ P bond energy is derived from the electrochemical potential difference of the proton across the coupling membrane.With respect to the alternative hypothesis for phosphorylation, the results impose grave restriction on a phosphorylation driven only by the free energy of a chemical intermediate, if this does exist at all.
The Critical Electric Potential Difference for Photophosphorylation
Authors: Junge Wolfgang 
Published: March 2005

The physical meaning of the observed critical electric potential difference necessary for photophosphorylation is discussed. An interpretation of this phenomenon on the basis of the equilibrium thermodynamic formulation of the chemiosmotic hypothesis requires a reversible ATPase system. Contrary to this, ATP hydrolysis experiments seem to confirm that the Mg++‐dependent ATPase system of class II‐chloroplasts is irreversible in the absence of SH‐compounds. This sheds doubt on the equilibrium thermodynamic interpretation of the critical electric potential difference for phosphorylation. However it can be shown, that the seeming irreversibility may be due to some trigger requirements of an intrinsically reversible ATPase system.This leads to an identification of the critical electric potential difference with the triggering level of the enzyme system.Two operational models for an ATPase system, whose activity is modulated by the electric potential difference, are derived. These account quantitatively for a set of experiments on the critical electric potential difference.
Reaction of Puromycin with Chemically Prepared Peptidyl Transfer RNA
Authors: DE Groot Nathan , Panet Amos , Lapidot Yehuda 
Published: March 2005

Chemically synthesized peptidyl‐tRNAphe reacts with puromycin when bound non‐enzymatically to Escherichia coli ribosomes in the presence of poly U. Guanosine triphosphate and G factor have no influence upon the puromycin reaction, when the magnesium ion concentration is 0.01 M or lower, but stimulate the puromycin reaction when the binding of peptidyl‐tRNA is carried out at higher magnesium ion concentration. In this stimulation β,γ‐methylene‐guanosine triphosphate cannot replace GTP, and fusidic acid inhibits the stimulation. The percentage of bound peptidyl‐tRNA which reacts with puromycin in the absence of G factor and GTP decreases upon increasing the magnesium ion concentration. From all these observations one can conclude that at magnesium ion concentrations below 0.01 M, peptidyl‐tRNA (such as Gly2‐Phe‐tRNA) binds preferentially to the donor site, but at higher magnesium ion concentrations (such as 0.025 M) the ribosomal aceptor site is preferred.Peptidyl‐tRNAPhe can react with puromycin in the absence of the proper mRNA at rather highmagnesium ion concentration (0.02 M and higher) but this interaction in the absence of mRNA may be not a common feature of other peptidyl‐tRNAs, except tRNAMetf.Phe‐tRNA interacts with puromycin but the rate of this interaction is much slower than that of peptidyl‐tRNAPhe such as Gly2‐Phe‐tRNA.
Zur Wirkung von Liganden auf das Assoziations‐Dissoziations‐Gleichgewicht des Methämoglobins der Flußneunaugen (Lampetra fluviatilis L.)
Authors: Behlke Joachim , Scheler Werner 
Published: March 2005

The dissociation‐association equilibrium of lamprey methemoglobin as a function of protein concentration, pH, and ligandation of the heme Fe3+ has been studied using sedimentation analysis.The sedimentation constant s°20,w of MetHb in the pH range 4.5 < pH < 10 amounts to 1.94 S leading to a calculated molecular weight of 17000 which corresponds to the Hb protomer.At pH 7.5 the MetHb · N3 complex is monomeric. Below pH 5.7 and at high protein concentration the dimer of 34000, s°20,w= 3.13 S, is formed, the dimerization being accompanied by an uptake of two protons per protomer: (a) 2 MetHb + 2 N3−+ 2 H+⇌ (H+· MetHb · N3)2. At high concentrations of protein and azide the association of MetHb · N3 becomes a function of pH only: (b) 2 MetHb · N3+ 2 H+⇌ (H+· MetHb · N3)2. The pK value of equilibrium (b) is found to be 6.7 pointing to a heme‐linked imidazole determining the equilibrium.As compared to the azide complex, other ligands, such as F− > OCN− > CN− > SCN−, favour the dimerization of lamprey MetHb to a lesser degree.Dimerization of the heme polypeptide chains in the MetHb‐ligand complexes and their association in DeoxyHb supposedly involves different aminoacids in the interface between the protomers.
On the Conformation of Phenylalanine Specific Transfer RNA Studies on Size and Shape of the Molecule by X‐Ray Small Angle Scattering
Authors: Pilz Ingrid , Kratky Otto , Cramer Friedrich , VON DER Haar Friedrich , Schlimme Eckhard 
Published: March 2005

The scattered X‐ray intensities from dilute solutions of tRNAphe (yeast) in 0.05 M Tris buffer at pH 7.5 were measured at 17°. The radius of gyration R (24.4Å), the molecular weight M (26100) and the volume V (41500 Å3) were determined.A comparison of experimental with theoretical scattering curves of different bodies shows that the shape of the molecule cannot be well represented by a simple triaxial body. The calculated scattering curves which fit the measured scattering data best are for an elongated body with two different cross‐sections.No significant change of X‐ray small angle scattering was observed on increasing the temperature from 17° to 40°. At higher temperature the radius of gyration is increased with increasing temperature and at 70° the molecule has a random coil conformation.
Studies on Methionyl Transfer RNA Synthetase from Escherichia coli K12 Amino Acid Composition and Relation of Sulfhydryl Groups to Enzyme Activities
Authors: Lawrence Françoise Jeane 
Published: March 2005

The purified methionyl‐tRNA synthetase isolated from Escherichia coli K 12 was shown to possess 24 cysteine residues, but no disulfide bridges from the amino acid composition and titration of the sulfhydryl groups with para‐mercuribenzoate and 5–5′‐dithio‐bis (2‐nitrobenzoic acid). All of these sulfhydryl groups were titratable with para‐mercuribenzoate, but in the presence of l‐methioninyl adenylate (a structural analogue of methionyl adenylate), eight of them were protected from reaction.The enzyme catalyzes two reactions: (I) the conversion of methionine and ATP to methionyl adenylate enzyme complex, and (II) the transfer of the methionine from the complex to the tRNA.Titration of the sulfhydryl groups with para‐mercuribenzoate in the presence of l‐methioninyl adenylate resulted in a loss of ability to transfer the methionine to tRNA (reaction II) while the ability to catalyse reaction I was essentially unaffected. This result demonstrated that: (a) there are different sites on the enzyme for the two reactions, and (b) different sulfhydryl groups in the enzyme are involved in reactions I and II.
Characterization of Protein Bound to Rapidly‐Labelled RNA in Polyribosomes from Rat Liver
Authors: Olsnes Sjur 
Published: March 2005

A complex of rapidly labelled RNA and protein that can be liberated from polysomes by treatment with EDTA has been characterized in attempts to establish whether it is derived from the nuclear particles (“informofers”) containing RNA of DNA‐like nucleotide composition.After short time of labelling with [3H]orotic acid, polysomes were isolated, either by a method involving Triton X‐100, or without any detergent (“free” polysomes). After treatment of polysomes with EDTA, the sedimentation rate of the rapidly‐labelled RNA was considerably higher than that expected for pure RNA. CsCl density gradient centrifugation demonstrated that the buoyant density of the labelled material had a value intermediate between that of pure RNA and protein. Treatment with sodium deoxycholate or with 0.5 M KCl, increased considerably the buoyant density of the labelled material, while that of the ribosomal sub‐units was only slightly affected. The results indicate that in polysomes the rapidly labelled RNA exists in a complex with protein that can be selectively removed by sodium deoxycholate or KCl.The proteins released by treatment with deoxycholate or with KCl were characterized by polyacrylamide gel electrophoresis. One of these proteins behaved similarly to the protein‐component of the nuclear particle containing RNA of DNA‐like base composition. It is suggested that this protein follows the rapidly labelled RNA (presumably messenger RNA) during its transfer from the nucleus to the polysomes.
Monosubstituted 2,2‐Dimethyl‐3‐Formyl‐L‐Thiazolidine‐4‐Carbonyl‐Insulins
Authors: Lindsay David G. , Shall Sydney 
Published: March 2005

The treatment of insulin in aqueous solution at pH 6.9 and 8.5, with the hydroxysuccinimide ester of 2,2‐dimethyl‐3‐formyl‐l‐thiazolidine‐4‐carboxylic acid leads to the incorporation of thiazolidine residues into the protein.Examination by DEAE‐Sephadex chromatography of the products formed shows the presence of three products. The relative amount of products formed depends upon the reaction conditions. Characterisation of these products by end‐group analysis, cellulose acetate electrophoresis, amino acid analysis of the performic acid‐oxidised chains and treatment with TPCK‐treated trypsin suggests that they are monosubstituted derivatives formed by reaction at each of the free amino groups of insulin.The effect of modification on the biological activity and crystallisation properties of the hormone is discussed as well as the application of the preparation of covalent heavy atom derivatives of proteins.
The So‐Called Non‐Histones from Acid‐Treated Calf Thymus Chromatin
Authors: Sonnenbichler Johann , Nobis Peter 
Published: March 2005

When chromatin from calf thymus is treated with dilute hydrochloric acid under mild conditions variable proportions of histones become bound to the DNA, thus becoming insoluble and appearing as non‐histones. This is confirmed by model experiments in which artificial mixtures of pure histones and DNA were treated with acid.The acid insoluble residual proteins formed are strongly bound (presumably covalently) to the DNA, but can be separated by density gradient centrifugation at pH 11.5. Some properties of these “non‐histones” are discussed. Their amino acid analyses are different from those of the histones. The differences, also recognizable in model experiments must originate from the mild acid treatment in presence of DNA and suggest modifications of amino acids. These “non‐histones” are considered to be masked histones, because after strong alkali treatment definite histone fractions can be recognized by electrophoreses.The conclusion is drawn that mild acid treatment of chromatin artificially produces “non‐histones”.
Purification of Rat Liver Acetyl Coenzyme A Carboxylase and Immunochemical Studies on its Synthesis and Degradation
Authors: Nakanishi Shigetada , Numa Shosaku 
Published: March 2005

Acetyl coenzyme A carboxylase from rat liver was isolated in homogeneous form as evidenced by sedimentation velocity experiments and Ouchterlony double diffusion analyses. The specific activity and biotin content of the purified enzyme preparation were similar to those of pure chicken liver enzyme isolated previously.Antibody against rat liver acetyl‐CoA carboxylase was prepared by injecting rabbits with the purified enzyme. With the use of this antibody, the mechanisms were studied by which the level of liver acetyl‐CoA carboxylase activity was varied in fasted rats, in those subsequently refed a fat‐free diet and in diabetic rats.Immunochemical analysis demonstrated that the wide variations in the level of acetyl‐CoA carboxylase activity in liver extracts derived from rats under the different dietary and hormonal conditions were accompanied by proportionate changes in the quantity of immunochemically reactive protein. This indicates that the changes in the activity level are determined by changing quantities of the carboxylase protein.Isotopic leucine incorporation studies showed that the relative rate of synthesis of liver acetyl‐CoA carboxylase was decreased 1.9‐fold and 1.7‐fold by fasting and diabetes, respectively, whereas increased 4.0‐fold by fat‐free refeeding. The rate of degradation of the carboxylase, expressed as half‐life, was found to be essentially the same in normal, refed and diabetic rats, i.e. 59, 55 and 59 h respectively, and accelerated in fasted rats, i.e. 31 h. Thus, the increase or decrease in the carboxylase quantity in refed or diabetic animals, which are presumably in a steady state, can be ascribed to a rise or fall in the rate of enzyme synthesis, whereas the decrease in the carboxylase quantity in fasted animals, which are not in a steady state, is due both to diminished enzyme synthesis and to accelerated enzyme degradation. On the basis of these results, it is discussed that the control of enzyme quantity by changes in the rate of enzyme degradation may play an important role when the animal deviates from a steady state for adjustment to a new environment.
The Structure of the Porcine Pancreatic Secretory Trypsin Inhibitor I
Authors: Tschesche Harald , Wachter Elmar 
Published: March 2005

Porcine pancreatic secretory trypsin inhibitor I (56 residues) was rendered sensitive to tryptic digestion by reduction and carboxymethylation. Nine tryptic fragments were formed by the action of trypsin. They were separated by taking advantage of the size fractionating and ion exchange properties of Bio Gel P‐2 in 0.01 N pyridine. The major tryptic peptides were purified on SE‐Sephadex C‐25.The amino acid sequence of each peptide was determined by a special technique of Edman degradation using p‐bromophenyl‐isothiocyanate. This reagent facilitated the identification of the extracted p‐bromophenyl‐thiohydantoines by mass spectrometry. The characteristic fragment and molecular ions are emphasized by a significant double peak of a mass difference Δm/e= 2, which is caused by the isotope ratio of the p‐bromosubstituent. In general this technique permitted up to thirteen consecutive steps of degradation and the unequivocal positioning of the amides.The complete amino acid sequence of the polypeptide trypsin inhibitor was determined.
Purification and Comparison of the N‐(5′‐Phosphoribosyl)anthranilic Acid Isomerase/Indole‐3‐glycerol Phosphate Synthetase of Tryptophan Biosynthesis from Three Species of Enterobacteriaceae
Authors: Mcquade John F. , Creighton Thomas E. 
Published: March 2005

A measure of evolutionary divergence between three species of the enterobacteriaceae was made by studying the physical properties of a protein common to all three, N‐(5′‐phosphoribosyl)‐anthranilic acid isomerase indole‐3‐glycerol phosphate synthetase, a bifunctional enzyme of the tryptophan biosynthetic pathway. The protein was purified to near homogeneity from Aerobacter aerogenes, Escherichia coli, and Salmonella typhimurium.The purified proteins were found to be very similar in their ultraviolet absorption spectra, fluorescence emission and excitation spectra, and molecular weights. Various determinations of the molecular weights varied from 4.4 to 5.1 × 104 daltons, and no significant differences were observed between the purified proteins and the enzymes in crude extracts. The electrophoretic behaviour of each of the three purified proteins on polyacrylamide gels with sodium dodecyl sulphate were similar and consistent with each enzyme consisting of a single polypeptide chain.Peptide patterns of each of the proteins were obtained following digestion with trypsin plus chymotrypsin. Close homology in primary structure between the proteins was suggested by the observation that approximately half the peptides of any two proteins were identical. Comparison with similar data from a previous study on the α subunit of tryptophan synthetase suggests that there has been no great difference in the rate of divergence of the α subunit and phosphoribosylanthranilate isomerase‐indole‐glycerol‐phosphate synthetase in the species studied.
The Kinetics of Yeast Hexokinase in the Light of the Induced Fit Involved in the Binding of its Sugar Substrate
Authors: DelaFuente Gertrudis , Sols Alberto 
Published: March 2005

The kinetics of the initial reaction rates of yeast hexokinase, both in the forward and in the backward direction, have been re‐examined in the light of recent findings concerning the properties of the ATPase activity of hexokinase and its modification by certain non‐phosphorylable analogues of the sugar substrates.A single pattern has been found in the double reciprocal plots even if the concentrations of both the acceptor and the donor substrates are varied over a wide range, with ITP as well as with ATP as donor substrates. A similar pattern has been found for the backward reaction.These results are interpreted as indicative that in the forward as well as in the backward reaction, the interconversion of the ternary complex of the enzyme with both substrates is the limiting step. This fact and the complex effect of glucose 6‐phosphate as an initially‐added product, prevents in principle the distinction between the possible kinetic mechanisms leading to the ternary complex. Nevertheless, taking into account the change in affinities for the nucleotide substrates specifically induced by certain sugars, it becomes possible to formulate a plausible hypothesis. It is postulated that binding of a sugar to an enzyme‐nucleotide complex results in an abortive ternary complex. Accordingly, formation of active ternary complexes in the hexokinase reaction requires the sequential addition of a nucleotide substrate to a binary complex of the enzyme with a sugar substrate.
Steroids in Germfree and Conventional Rats
Authors: Eriksson Håkan 
Published: March 2005

Radio‐gas chromatography and gas chromatography‐mass spectrometry were used to study unconjugated metabolites of administered [4‐14C]corticosterone and [4‐14C]pregnenolone in faeces from germfree and conventional female rats. 3α‐Hydroxy‐5α,17α‐pregnan‐20‐one, 3α‐hydroxy‐5α,17β‐pregnan‐20‐one, 3β‐hydroxy‐5α,17β‐pregnan‐20‐one, 3β,15β‐dihydroxy‐5α‐pregnan‐20‐one, 3β,15α‐dihydroxy‐5α‐pregnan‐20‐one and 3α,16α‐dihydroxy‐5α‐pregnan‐20‐one were characterized as metabolites of pregnenolone whereas 3α,20β‐dihydroxy‐5α‐pregnan‐11‐one and 3β,20β‐dihydroxy‐5α‐pregnan‐11‐one were identified as metabolites of corticosterone in the conventional rats. Two other 3,15‐dihydroxypregnan‐20‐one isomers, tentatively identified as the 3α,5α,15α(and 15β) epimers, were also found. In addition 3β‐hydroxy‐5‐androsten‐17‐one, 5α‐androstane‐3β,17β‐diol, 5α‐androstane‐3α,7α,17β‐triol, 3α(and 3β),19‐dihydroxy‐5α‐pregnan‐20‐one and 5α‐pregnane‐3α(and 3β),20α‐diol were recovered in the free steroid fraction in faeces from conventional female rats. The amounts of these steroids were too small to permit a study of the degree of labelling.Although some radioactivity was present in the free steroid fraction from the germfree animals no steroid could be identified in this fraction. The findings are discussed with particular reference to enzyme activities of the intestinal flora.
Glycine Formation via Threonine and Serine Aldolase. Its Interrelation with the Pyruvate Formate Lyase Pathway of One‐carbon Unit Synthesis in Clostridium kluyveri
Authors: Jungermann Kurt A. , Schmidt Wilhelm , Kirchniawy F. Hans , Rupprecht Eckhard H. , Thauer Rudolf K. 
Published: March 2005

14C‐labeling experiments with growing Clostridium kluyveri have shown that two pathways each are operative for glycine and one‐carbon unit synthesis: about two‐thirds of the cell's glycine is formed from threonine and one third from serine; serine simultaneously yields about a quarter of the cell's C1‐units, while the remaining three‐quarters are derived from CO2via the pyruvate carboxyl group.The key enzymes, threonine aldolase and pyruvate formate lyase as well as serine aldolase interrelating glycine and C1‐unit synthesis, could be demonstrated in cell‐free lysates in activities sufficient to account for the anabolic requirements during growth. The substrate specificity, cofactor requirements and Km values indicate that threonine aldolase and serine aldolase are two separate, constitutive and pyridoxal phosphate dependent enzymes.
An Optical Rotatory Dispersion Study of 6‐Phosphogluconate Dehydrogenase
Authors: Rippa Mario , Pontremoli Sandro , Fasella Paolo 
Published: March 2005

The optical rotatory dispersion of purifed 6‐phosphogluconate dehydrogenase in the 500 to 195 nm region was examined in the presence and absence of its coenzymes and substrates. Identical curves were obtained in all cases.In particular, coenzyme binding does not cause an extrinsic Cotton effect. In this respect, 6‐phosphogluconate dehydrogenase, like several other dehydrogenases, differs from alcohol dehyudrogenase.The ultraviolet portion of the optical rotatory dispersion curve suggest that 6‐phosphogluconate dehydrogenase may contain other structures besides α‐helix, β‐structure and random coil.
Action Patterns of Phosphorylase and Glycogen Synthetase on Glycogen
Authors: Parodi Armando J. , Mordoh José , Krisman Clara R. , Leloir Luis F. 
Published: March 2005

The action patterns of liver and muscle glycogen synthetases and of muscle phosphorylase b on glycogen samples of different molecular weight and on β‐amylase limit dextrins were studied. For this purpose a method for measuring the number of newly added glucose residues that are at non‐reducing ends was developed.It was found that glucose transfer to the non‐reducing ends of glycogen catalyzed by liver glycogen synthetase and muscle phosphorylase followed a Poisson distribution.The number of outer chains in the glycogen molecules available to both enzymes appeared to be smaller than the actual number of outer chains in the polysaccharide. The number of such available chains diminished as the glycogen was heavier. For the same glycogen sample, the number of available chains to phosphorylase appeared to be equal or smaller than that to glycogen synthetase.It was found that muscle phosphorylase transferred 1.2 to 1.4 glucose moieties successively per outer chain, independently of the molecular weight of the glycogen.The number of glucose units added successively to the non‐reducing ends of glycogen by liver glycogen synthetase increased from 1.7 to 6.8 with the molecular weight of the polysaccharide.Both phosphorylase and liver glycogen synthetase transferred more glucose units in a repetitive way to the same outer chain of the β‐amylase limit dextrin than to the same outer chain of the undegraded glycogen.Muscle glycogen synthetase transferred a greater number of glucose units successively per outer chain of glycogen than the liver enzyme.