Showing papers by "Weizmann Institute of Science published in 1969"
TL;DR: The intrinsic viscosity of sonicated calf thymus DNA (molecular weight 4-5 × 105) increases and sedimentation constant decreases, with increasing binding of proflavine at 0.2 ionic strength and at 25°C.
Abstract: The intrinsic viscosity of sonicated calf thymus DNA (molecular weight 4–5 × 105) increases and the sedimentation constant decreases, with increasing binding of proflavine at 0. 2 ionic strength and at 25°C. The measurements correspond to a linear increase in length of the almost rodlike DNA molecules with the amount of proflavine bound; independent calculations from viscosity and sedimentation measurements yield almost identical results. Over the range of r (moles of proflavine bound per moles of nucleotides) equal to zero to r = 0.13, the length increases by about 20%. This extension is compatible with the intercalation hypothesis proposed by Lerman. Density increments at various values of r, at constant chemical potential of diffusible solutes, were determined. It was also found that, in addition to the known isosbestic point of DNA-proflavine complexes at 455.5 mμ, an additional isosbestic point exists at 225.5 mμ; this proved extremely useful for the evaluation of binding studies.
920 citations
TL;DR: No inter ference with cellular function is observed as shown by almost complete regeneration of GSH after incubation with glucose at 370, and no alteration in hemoglobin, osmotic fragility or cell density is found.
507 citations
TL;DR: A rapid refinement procedure capable of deriving the stable conformation of a macromolecule from experimental model co-ordinates is presented and a set of non-bonded potential functions applicable to the equilibrium of a folded protein in an aqueous medium is described and tested on myoglobin.
409 citations
394 citations
TL;DR: About 85 per cent of binding sites for the protein concanavalin A that are exposed on the surface membrane of transformed cells, are in a cryptic form on normal cells.
Abstract: About 85 per cent of binding sites for the protein concanavalin A that are exposed on the surface membrane of transformed cells, are in a cryptic form on normal cells. The change in structure of the surface membrane resulting in the exposure of surface sites may produce the change in cellular regulatory mechanism that is associated with transformation.
289 citations
247 citations
TL;DR: This chapter reviews a series of experiments that utilize muscle cell cultures as a model for studying some of the inherent properties of differentiating cells and shows that the changes, which take place in the growth characteristics during establishment of cell lines, may be distinct from the differentiation characteristics of these lines.
Abstract: Publisher Summary This chapter reviews a series of experiments that utilize muscle cell cultures as a model for studying some of the inherent properties of differentiating cells. A main outcome of the experiments is the establishment of myogenic cell lines that are able to multiply for extended periods in culture and retain their capacity to differentiate. It is not clear why some of the attempts to establish myogenic lines resulted in the loss of the cells by degeneration and cessation of multiplication whereas others were successful. This experience is common for many kinds of mammalian or avian cells serially passaged in vitro. The establishment of myogenic cell lines is of special interest with relevance to this phenomenon as it shows that the changes, which take place in the growth characteristics during establishment of cell lines, may be distinct from the differentiation characteristics of these lines. The possibility of cloning and thus performing analyses and experiments on homogeneous populations of one kind of cell makes this system valuable and versatile for studying many aspects of cell differentiation. Differentiated primary cultures always contain a population of mononucleated cells that do not participate in fusion. The relative proportion between the amount of mononucleated and multinucleated cells is variable and is influenced by culture conditions. Also, under identical culture conditions, clones produced by different cell lines differ considerably in their mononucleated cell content.
213 citations
TL;DR: This review of the present situation of glutathione ends with some suggestions for the future.
Abstract: Glutathione plays many parts in living organisms, and new methods for the oxidation of this tripeptide reveal some of them This review of the present situation ends with some suggestions for the future
183 citations
TL;DR: A method is given for finding those solutions of a transportation problem which minimize the total time necessary for transporting goods from the suppliers to the consumers.
Abstract: A method is given for finding those solutions of a transportation problem which minimize the total time necessary for transporting goods from the suppliers to the consumers. Several extensions of the model are presented.
148 citations
TL;DR: It is suggested that the conformation found for the polytripeptide may be representative of the structure of collagen as a whole.
137 citations
TL;DR: In this article, the relaxation time for the fluctuations in the direction of the magnetization vector is calculated for very fine, single-domain ferromagnetic particles which have a uniaxial (shape or crystalline) anisotropy.
Abstract: The relaxation time for the fluctuations in the direction of the magnetization vector is calculated for very fine, single-domain ferromagnetic particles which have a uniaxial (shape or crystalline) anisotropy. A magnetic field is assumed to be applied parallel to the easy magnetization axis, and the relaxation time is computed for various magnitudes of this field. It is found that the commonly used approximation for high-energy barriers is about as justified as in the case of zero magnetic field, down to barriers of the order of $\mathrm{kT}$.
TL;DR: Calculation of intensities for various models for the DNA-spermine complex indicates that no one model can account for the observed X-ray pattern, but the assumption of spermine in the small groove of DNA as well as in intermolecular cross-links, or of an even greater variety of modes of attachment between DNA and s permine, does lead to satisfactory agreement between calculated and observed intensities.
TL;DR: In this article, an electric charge moving in the field of a magnetic charge is discussed and solved by algebraic methods which exhibit the direct relation between charge quantization and angular momentum.
TL;DR: It was found that the chicken pepsin derivative obtained by reaction with 5,5'-dithiobis(2-nitrobenzoic acid) retained 86% of the enzymic activity, which shows that it is a less acidic protein than other pepsins so far investigated.
TL;DR: Several polytripeptide and polyhexapeptide models of collagen have the same triple helical conformation with one NH…O interchain H bond per tripeptides, suggesting that collagen itself probably has this structure.
Abstract: Several polytripeptide and polyhexapeptide models of collagen have the same triple helical conformation with one NH…O interchain H bond per tripeptide. Collagen itself probably has this structure.
TL;DR: Nuclear satellite DNA of high specific activity labelled with [ 3 H- methyl ]- l -methionine and 32 P was isolated from newborn mice and from cultured mouse embryo cells and found to have more than twice the molar concentration of 5-methylcytosine than the main band of nuclear DNA.
TL;DR: In this paper, the M 2 tide was solved in a realistic model of the world oceans based on the observed topography of the ocean bottom and a fine computational grid was required to assure numerical convergence of the solution.
Abstract: Laplace’s tidal equations were solved for the M 2 tide in a realistic model of the world oceans based on the observed topography of the ocean bottom. When friction was neglected, the theoretical tides came out high, but of the right order of magnitude. The tidal heights proved to be sensitive to changes in the configuration of the coastline, indicating a state of near resonance. However, the positions of the amphidromic centres remained stable and were located close to the empirically deduced amphidromes. A fine computational grid was required to assure numerical convergence of the solution. A solution was also carried out with friction included, on the assumption of a bottom frictional force proportional to the first power of the velocity. For a coefficient of friction appropriate to tidal currents in shallow waters, the theoretical tidal heights came out in fair agreement with the observed values. With friction included, the solution proved insensitive to changes in the configuration of the coastline, and the numerical convergence was also improved. The resulting rate of tidal dissipation was higher than the observationally deduced values, but the excess is within the uncertainty of the latter. Our solution for the tide is given in figure 10, and the corresponding tidal current chart in figure 12. Figure 11 gives a comparison of the Middle South Atlantic amphidrome, which was derived from theory, with tidal observations in island stations.
TL;DR: 5′-(4-Aminophenyl-phosphoryl)-uridine-2′(3′)-phosphate was synthesized and coupled to Sepharose by activation with cyanogen bromide and used as a specific adsorbent for purification of ribonuclease A by affinity chromatography.
Abstract: 5′-(4-Aminophenyl-phosphoryl)-uridine-2′(3′)-phosphate was synthesized and coupled to Sepharose by activation with cyanogen bromide. This conjugate was used as a specific adsorbent for purification of ribonuclease A by affinity chromatography. Totally reduced and oxidized RNase preparations which are enzymatically inactive were not adsorbed or retarded by the RNase-specific column, while S-protein is strongly retarded.
TL;DR: The different labeling of young, old, and RDE-treated human and rabbit red cells was correlated with their electric mobility and agglutinability by poly-L-lysine, and the contradiction between the apparent similarity in charge density of human and Rabbit red cells as estimated by density of iron particles and the markedly lower electric mobility of rabbitred cells is discussed.
Abstract: Human and rabbit red blood cells, separated into "young" and "old" age groups by differential flotation on phthalate esters, were fixed with glutaraldehyde and labeled with colloidal ferric oxide. Electron micrographs of thin sections of young cells showed a uniform and dense depostion of positive iron particles. Old cells showed particles deposited irregularly, leaving unlabeled gaps on the membrane surface. Red cells incubated with 10 units/ml receptor-destroying enzyme (RDE) demonstrate a reduced labeling, similar to that of old cells. After neuraminic acid had been removed from red cells by 20 units/ml RDE, no iron particles were found on membrane surfaces. The different labeling of young, old, and RDE-treated human and rabbit red cells was correlated with their electric mobility and agglutinability by poly-L-lysine. The contradiction between the apparent similarity in charge density of human and rabbit red cells as estimated by density of iron particles and the markedly lower electric mobility of rabbit red cells is discussed.
TL;DR: The structure of polytr-prolyl-glycyl-glycine has been found to consist of helices which resemble the individual strands of the triple helix models for collagen, but the h eli ces are not coiled about eac h other as in the collagen models.
TL;DR: The stable isotopic composition (18O and 2H) of the mineral water sources in the Jordan Rift Valley suggests that these sources evolved through a two stage mixing process as mentioned in this paper, and it is postulated that sometime in the past waters of a slightly evaporated seawater lake had mixed with the prevailing groundwaters, to form different fossil brine pockets along the Rift Valley's floor.
TL;DR: The results indicate that the surface structure of transformed cells can completely revert to the structure found in normal cells, as measured by reversion to the cryptic form of sites for Con.
Abstract: The cell surface structure of variants from polyoma-transformed cells grown in animals and then cultured in vitro, which show a reversion of in vitro properties of transformation without losing the ability to synthesize the polyoma-specific nuclear tumor (T) antigen, has been studied by using the carbohydrate-binding protein concanavalin A (Con. A) which interacts with sites on the cell surface membrane. Transformed cells are agglutinated by this protein. Normal cells, whose sites for Con. A are mainly in a cryptic form, are agglutinated only after they have been treated with trypsin. It has been shown that some variants showed a partial, and others a complete, loss of agglutinability by Con. A, and that the agglutinability of these variants was restored by treatment with trypsin. Compared to the parental transformed cells, all the variants showed the same decrease in cloning efficiency in fluid medium and soft agar, and in saturation density. The results indicate that the surface structure of transformed cells can completely revert to the structure found in normal cells, as measured by reversion to the cryptic form of sites for Con. A; that the synthesis of T antigen, presumably due to integrated virus DNA, is by itself not sufficient to prevent this reversion; that variants with this reversion in cells grown in vitro can have a high degree of tumorigenicity in animals; and that a threshold for the number of exposed surface sites for Con. A has to be exceeded before the cells express the in vitro properties of transformation.
Reversion de la Surface des Cellules Transformees
La structure de la surface cellulaire de mutants de cellules de polyome transformees prelevees sur des animaux puis cultivees in vitro — ou l'on observe une reversion des proprietes de transformation in vitro ainsi que la synthese de l'antigene (T) des tumeurs nucleaires specifiques du polyome — a ete etudiee au moyen de la concanavaline A (Con. A) — proteine de liaison glucidique — qui agit sur les sites de la membrane de la surface cellulaire. Les cellules transformees s'agglutinent en presence de cette proteine. Les cellules normales, dont les sites reagissant a la Con. A sont generalement de forme cryptique, ne s'agglutinent qu'apres un traitement a la trypsine. Il a ete demontre que certains mutants presentent une perte partielle et parfois totale d'agglutinabilite par la Con. A, et que l'agglutinabilite de ces mutants est retablie par traitement a la trypsine. Par rapport aux cellules meres transformees, tous les mutants presentent la měme diminution de l'efficacite de clonage dans un milieu liquide et dans la gelose molle, ainsi que de la densite de saturation. Les resultats montrent 1) que la structure de la surface des cellules transformees peut redevenir exactement la měme que celle des cellules normales, comme on l'a mesure par retour a la forme cryptique des sites reagissant a la Con. A; 2) que la syntheese de l'antigene T, sans doute due a l'ADN a virus integres, ne suffit pas en elle-měme a empěcher cette reversion; 3) que les mutants presentant cette reversion dans des cellules cultivees in vitro peuvent ětre fortement tumorigenes chez l'animal; et 4) qu'il faut depasser un seuil — quant au nombre de sites de surface exposes a la Con. A — avant que les cellules acquierent les proprietes de transformation in vitro.
TL;DR: The key step is the use of 2 M LiCl, which separates ribosomal RNA from tRNA rapidly and completely, and yields tRNA as active as the best preparations that have been obtained with other methods.
TL;DR: It is suggested that the uncoupling produced by the compounds used in this work is of the same type as that induced by the antibiotics, gramicidin and nigericin, both of which were suggested to increase the membrane permeability to both protons and cations.
Abstract: A general mechanism is presented for uncoupling of chloroplasts by compounds or combination of compounds which increase membrane permeability to both protons and alkali metal cations.
Agents which supposedly increase the membrane permeability to protons only, such as 2,4-dinitrophenol and carbonyl cyanide p-trifluoromethoxy phenylhydrazone (FCCP) (at low concentrations), did not uncouple chloroplasts. Similarly, the antibiotics valinomycin, and nonactin and the synthetic compound LR6-125, which apparently increase only the cation permeability of membranes, did not uncouple. However, combinations of dinitrophenol or of low concentrations of FCCP with anyone of the cation permeability inducing agents, led to full uncoupling of the chloroplasts. Studies on the passive permeability properties of the grana membrane, support the assumption that combinations of dinitrophenol or FCCP (at low concentrations), with valino-mycin or nonactin or LR6-125, increase the membrane permeability to both proton and cations. High concentrations of FCCP (10 μM) which alone uncoupled chloroplasts, also appeared to increase the permeability of the membrane to both protons and to cations, while low concentrations of FCCP, which did not uncouple alone, sufficed to increase the membrane permeability to protons. It is suggested that the uncoupling produced by the compounds used in this work is of the same type as that induced by the antibiotics, gramicidin and nigericin, both of which were suggested to increase the membrane permeability to both protons and cations.
TL;DR: It is of particular interest, however, that ribosomes that have been inactivated toward non-enzymatic binding are active at 0’ in the enzymaticbinding reactions mediated by initiation factors or transfer factor T, even if they have not been previously heated.
TL;DR: Electrophoretic studies indicated that alkylation of the partially reduced derivative yielded a unique molecular species (3-RCM papain) in which one specific disulfide bond had been split, rather than a mixture of unreduced and open chain papain.
TL;DR: The density and distribution of electric charge on the surface of rabbit bone marrow cells was visualized by electron microscopy after the cell surfaces had been stained with charged colloidal iron particles.
Abstract: The density and distribution of electric charge on the surface of rabbit bone marrow cells was visualized by electron microscopy after the cell surfaces had been stained with charged colloidal iron particles. Expulsed erythroid nuclei are less negatively charged than any other cell in the bone marrow. They carry from about one-half to one-third of the charge density on the remaining future reticulocyte. The reduction in the surface charge density is already apparent when the nucleus is partially expulsed. Practically no positive charge was found on its surface or on the surface of any other bone marrow cell. The possibility that the reduced negative charge on the surface of expelled erythroid nuclei is one of the means by which the macrophage distinguishes it from other bone marrow cells is discussed.
TL;DR: In this paper, the ambiguities of complex phase shift analysis made for a definite number of partial waves and given energy are dealt with, and all ambiguous sets of phase shifts are physically acceptable.