Molecules Of Different Sizes Research Articles

Molecular size of plasmid R18 and its substituted variants inEscherichia coli cells

R-substituted plasmids (R18Arg) obtained from plasmid R18 and capable to convert Arg- strains E coli to Arg+ strains at the expense of genetic material mobilized from P. aeruginosa chromosome are physically unstable and exist as molecules of different size. It was shown that the physical size of plasmid R18Arg is 3--5 megadaltons greater than those of plasmid R18.

A vegetalizing inducing factor isolation and chemical properties

A vegetalizing factor which induces the formation of endodermal and mesodermal organs in amphibian gastrula ectoderm was purified from chicken embryos. Preparative sodium dodecyl sulfate polyacrylamide electrophoresis and gel permeation chromatography on Sephadex with different eluants were employed. In buffer containing 6 M urea the molecular weight of the factor was estimated to about 28 000–30 000. In buffer containing sodium dodecyl sulfate (SDS) the factor partially dissociates to smaller polypeptide chains. Because an equilibrium between molecules of different size is established, SDS-containing buffers are not suitable preparative purposes. In 50%–70% formic acid the factor completely dissociates into smaller peptide chains ( M r about 13 000–15 000). Furthermore, very little adsorption of the factor to the gel matrices or glass surfaces is observed in formic acid. The final purification can be achieved by high-performance gel permeation chromatography with glycerolpropyltreated silica gel as column packing and 50% formic acid as eluant.

Thermodynamics of mixtures of hexane and heptane isomers with normal and branched hexadecane

Molar excess mixing enthalpies h E , Gibbs free energies g E and hence entropies s E have been obtained using calorimetry and the vapor sorption method at 25°C for hexane isomers+2,2,4,4,6,8,8-heptamethylnonane, a highly branched C 16 . The h E and g E are negative while Ts E are positive, but small. The values are explained by the Prigogine-Flory theory through negative free volume contributions to h E and Ts E , counterbalanced in the case of Ts E by the positive combinatiorial Ts E for mixing molecules of different size. No contribution is seen from the interaction between methyl and methylene groups. The excess quantities are also obtained for hexane and heptane isomers mixed with n-hexadecane. Values of h E and Ts E are now strongly positive, while those of g E are only slightly less negative. The interpretation requires two recently advanced contributions in addition to those of the Prigogine-Flory theory: 1) a decrease of order when correlations of orientations between n-C 16 molecules in the pure liquid are replaced in the solution by weaker correlations whose strengths depend on the shapes of the lower alkane isomers. For lower alkane isomers of the same shape, but highly sterically hindered, h E and Ts E are small, manifesting, 2) a negative contribution, ascribed to a rotational ordering of n-C 16 segments on the sterically-hindered molecule. Enthalpy-entropy compensation is observed for these new contributions, arising from their rapid fall-off with increase of temperature.

Molecular Theory of Liquid Adsorption Chromatography

Abstract A statistical-mechanical theory, based on a lattice model, has been developed to address the molecular mechanism of retention and selectivity in both normal-phase and reversedphase liquid adsorption chromatography. The model is a natural “competitive-equilibrium” one, where possible contributions from solvent-solvent and solute-solvent interactions, and, hence, from solution nonideality, are not neglected. Homogeneous and heterogeneous adsorbent surfaces, single-solvent and binary mixed-solvent mobile phases, and solute molecules of different size and shape are treated. Practical applications of the theory are presented to demonstrate its utility and significance. For homogeneous adsorbents and neat solvents, the molecular energetics of retention and selectivity are examined, with special emphasis on the effects of solute size and shape, and, relatedly, the modes of solute adsorption. Separations of geometrical isomers and homologous series in real and simulated chromatographic processes are inve...

Permeability of the Cell-to-Cell Membrane Channels in Mammalian Cell Junction

The channels in the junctions of various mammalian cell types--primary cultures and lines--were probed with a series of linear fluorescent amino acid and peptide molecules of different size and charge. Permeability is limited by probe size and electronegativity, these two factors apparently being related reciprocally. In respect to both factors, mammalian junctional channels are more restrictive than insect channels; hence the mammalian channels are narrower, more polar, or both. The channels of the various mammalian cell types differed slightly from each other; in some types the serum of the culture medium affected the channel permeability.

The Functional Size of the Primary Complement Lesion in Resealed Erythrocyte Membrane Ghosts

Abstract We compared the susceptibility to complement (C) lysis of resealed sheep erythrocyte membrane ghosts (M) with that of intact erythrocytes (E). E were lysed hypotonically in the presence of radiolabeled marker molecules that were entrapped in the M during resealing. C-induced lysis was measured by the amounts of 3H-sucrose and hemoglobin released from antibody (A)-treated M (MA) and E (EA), respectively. The degree of lysis produced by different concentrations of guinea pig serum was identical for both systems. Treatment with C8 and C9 resulted in identical levels of lysis of MAC1-7 and EAC1-7; in addition, similar binding of radiolabeled C8 by MAC1-7 and EAC1-7 was obtained. These results demonstrate that the reactivity of M with A and C is similar to that of intact E. To determine the effective pore size of the primary C lesion, radiolabeled molecules of different size were entrapped in the M, and their release by A and C as a function of time or C concentration was investigated. An excess of guinea pig, human, or rabbit serum produced complete release of 3H-sucrose and 3H-inulin at the end of 60 min of incubation at 37°C, but the release of 125I-ribonuclease (RNase) proceeded at a slower rate. The rates of release were directly related to the size of the marker molecules and the concentrations of C used. With 125I-ovalbumin and larger molecules (hemoglobin, 125I-bovine serum albumin, 125I-urease, and 125I-thyroglobulin) the release was of low level and similar for all molecules. The release in controls with heat-inactivated (56°C, 30 min) guinea pig and human serum or C6-deficient rabbit serum was less than 10% for all markers after 60 min of incubation at 37°C. The patterns of release of marker molecules from MAC1-7 reacted with C8 and C9 were similar to those of EA treated with serum as source of C. However, the differences in rate of release of the various markers were more pronounced. Incubation of MAC1-7 alone resulted in a 10 to 12% release of all markers after 60 min at 37°C, and incorporation of C8 produced an additional 10% increase in release. Because RNase and smaller molecules can readily diffuse across C-treated M, we conclude that the size of the primary C lesion has a minimal diameter of 40 Å. It is also possible that resealing of larger primary C lesions occurs rapidly and thus markedly reduces the egress of large molecules from the lysing M.

A multiple plasmid-containing Escherichia coli strain: Convenient source of size reference plasmid molecules

A strain of Escherichia coli is described that contains eight plasmid species ranging in size from 1.36 × 10 6 to 35.8 × 10 6 daltons. This strain can be employed as a single source of covalently closed circular deoxyribonucleic acid molecules of different sizes for use as references in agarose gel electrophoretic analysis.

The Size of the Lesion Induced by the Alternative Complement Pathway on Human Erythrocyte Membranes

Abstract By using a direct approach we have demonstrated previously that the classical C pathway produces on sheep erythrocyte membranes functional lesions of about 4 nm diameter. We have now investigated the size of the lesions induced on human erythrocyte membranes by activation of the alternative C pathway. Human red cells were treated with 2-aminoethylisothiouronium bromide (AET) to increase their reactivity with C. They were then lysed hypotonically in the presence of radiolabelled marker molecules of different size which were incorporated into the membranes ghosts during resealing. The membranes were finally treated with human serum together with inulin particles to activate the alternative pathway. This resulted in identical % release of 3H-sucrose from membrane ghosts and of hemoglobin from AET-treated intact erythrocytes. No release of 125I-ovalbumin or 125I-BSA was obtained from membrane ghosts. The release of soluble 3H-inulin was slightly slower and that of 125I-RNase markedly slower than that of 3H-sucrose.

Matrix Raman spectra of Ag 2 and Ag 3

Silver molecules of different sizes have been synthesized by co-condensation of a monatomic silver beam with an excess of Kr gas on a cooled copper target. Several Raman bands below about 220 cm −1 are found. The two strongest, at 194 ± 0.5 cm −1 and 120.5 ± 0.5 cm −1, could clearly be assigned to Ag 2 and Ag 3 respectively. The existence of only one band for Ag 3 strongly suggests this molecule is linear.

Distribution of n-paraffins in sea-grasses, benthic algae, oysters and recent sediments from Terminos Lagoon, Campeche, Mexico.

To determine the presence of petroleum hydrocarbons in the components of a marine ecosystem one must first evaluate the relative quality of the hydrocarbons biosynthesized in the system. In this way it is possible to distinguish some of the biogenic hydrocarbons series occurring in marine organisms and sediments from those of fossil origin (Clark and Finley, 1973). Organisms possess specific biosynthetic pathways which favor the production of hydrocarbons in preferred size ranges. Crude oils and oil products, on the other hand, are wide range mixtures that contain molecules of different sizes in fairly even distribution. The primary purpose of this study is to establish the distribution of biogenic n-paraffins in marine ''sea-grasses,'' benthic algae, invertebrates and recent sediments from Terminos Lagoon, Campeche, Mexico. Considering the uncontaminated nature of this coastal region the results of this study will provide a basis for the assessment of future man-induced alterations.

Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects

Smirnova, N.A., 1978. Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects. Fluid Phase Equilibria, 2: 1–25. A multilayer lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects is developed. The system is treated in the grand canonical ensemble on the basis of the quasi-chemical approximation. The results relate to the mixtures of monomers + flexible r-mers, where all r segments of r-mer may be different and the surface of monomer molecules and r-mer segments may be inhomogeneous (thus, the systems with polar components, associated solutions among them, are in the range of applicability of the model). The monomer + r-mer system is described based on the modified model for the multicomponent system formed by monomeric particles with strong directed interactions. Equations for the concentration profile and for the average molecular orientations, with respect to the surface, are derived; the formulae for the adsorption and surface tension are given. The surface properties calculated on the basis of the model for three monomer + dimer systems are in satisfactory agreement with the experimental data. The entropy contribution to the surface tension of pure r-mer composed of identical segments is reported for r = 2, 4, 6, 8, 12 and for different lattice parameters. The model can be generalized to mixtures of r-mers + l-mers.

Measurements of Intestinal Permeability Using Low Molecular Weight Polyethylene Glycols (PEG 400): I. Chemical analysis and biological properties of PEG 400

A new approach to the measurement of intestinal permeability in man has been developed, using low molecular weight polyethylene glycol (PEG 400) as probe molecules. PEG 400 (range of molecular weight 232 to 594) is a mixture of water-soluble molecules of different sizes which can be extracted readily from biological fluids and analyzed by gas-liquid chromatography. PEG 400 is nontoxic, not degraded by intestinal bacteria, not metabolized after absorption, and rapidly excreted in urine. The different-sized molecular components cross the intestinal epithelium at different rates, allowing characterization of the passive permeability properties of the mucosa.

Effect of non-mesomorphic plate-like solutes on thermal behavior of liquid crystalline solvents

Binary mixtures of plate-like molecules of different size and shape with various rod-like mesomorphic solvents are studied. In several cases an “ unusual” increase of the isotropic to nematic transition temperature is observed and, when the solubility permits it, a maximum in the NI equilibrium curve (of temperature-concentration diagrams) appears. We try to explain this effect by comparison with previous works and a short discussion on the possible influence of structural parameters of the compounds in different mixtures is also given.

The 5'-termini of heterogeneous nuclear RNA: a comparison among molecules of different sizes and ages.

The composition of the 5' polyphosphorylated and capped termini of pulse labeled hnRNA from mouse L cells was analyzed by two-dimensional electrophoresis. Purine tri- and diphosphates: pppG, pppA, ppG and ppA; as well as four varieties of cap structure: m7GpppXm, Xm = Gm, (m6) Am, Cm and Um, were detected. With increasing labeling time the relative proportion of hnRNA molecules with tri- and diphosphorylated 5' ends decreases and the relative proportion of capped hnRNA increases, indicating that caps are metabolically more stable than the polyphosphate termini. About half of the hnRNA molecules that are labeled within 2 hr have capped ends. This finding, together with results of earlier kinetic and structural studies, implies that a relatively high proportion of the labeled hnRNA molecules are mRNA precursors. Large hnRNA molecules exhibit a higher proportion of capped ends and a lower proportion of 5'-triphosphate ends as compared to small hnRNA. Given the lower stability of triphosphate termini relative to caps, this result may mean that capping of some hnRNA molecules can occur before the completion of transcription.

Fragmentation of chromatin with 125I radioactive disintegrations

The DNA in Chinese hamster cells was labeled first for 3 h with [3H]TdR and then for 3 h with [125I]UdR. Chromatin was extracted, frozen, and stored at -30 degrees C until 1.0 X 10(17) and 1.25 X 10(17) disintegrations/g of labeled DNA occurred for 125I and 3H respectively. Velocity sedimentation of chromatin (DNA with associated chromosomal proteins) in neutral sucrose gradients indicated that the localized energy from the 125I disintegrations, which gave about 1 double-strand break/disintegration plus an additional 1.3 single strand breaks, selectively fragmented the [125I] chromatin into pieces smaller than the [3H] chromatin. In other words, 125I disintegrations caused much more localized damage in the chromatin labeled with 125I than in the chromatin labeled with 3H, and fragments induced in DNA by 125I disintegrations were not held together by the associated chromosomal proteins. Use of this 125I technique for studying chromosomal proteins associated with different regions in the cellular DNA is discussed. For these studies, the number of disintegrations required for fragmenting DNA molecules of different sizes is illustrated.

Isopycnic Centrifugation of Thyroid Iodoproteins: Selectivity of Endocytosis

Isopycnic centrifugation in RbCl was shown to be an effective method both for evaluating the iodine content of thyroglobulin labelled in vivo and for the fractionation of thyroglobulin molecules as a function of their iodine content. Iodination and degradation of thyroid iodoproteins were studied by this method and by zonal centrifugation in sucrose density gradients. Based on these methods it was shown that iodination in vivo is a selective process, 19-S and poorly iodinated thyroglobulin having a higher reactivity toward iodine than 27-S and iodine-rich thyroglobulin. The disappearance of iodoproteins from the thyroid was evaluated by equilibrium, labelling the iodoproteins, blocking iodine incorporation with thiourea derivatives and observing (by sucrose gradient and by RbCl isopycnic centrifugation) at different times the properties of the remaining molecules. Among molecules of different size (19-S and 27-S) and among molecules of the same size (19 S) but different iodine content it was shown that reabsorption from the thyroid gland occurred at the same rate. It was concluded, therefore, that the degradative pathway is essentially a random, non-selective process. Newly iodinated (pulse-labelled) iodoproteins were degraded faster than preexisting molecules. Among the pool of those newly iodinated thyroid proteins, 27-S molecules were reabsorbed faster than 19-S molecules and iodine-rich thyroglobulin molecules were reabsorbed faster than the iodine-poor ones. Since iodination in vivo occurs as repeated pulses of iodine incorporation, it is suggested that this latter phenomenon is a regulatory mechanism which minimizes degradation of molecules which are iodine-poor and have a lower hormonal content.

The effect of cerebrospinal fluid pressure on the size of drainage pathways.

The cerebrospinal fluid drainage pathways were studied using labeled molecules of different sizes. Following determination of the limiting size, the cerebrospinal fluid pressure was raised above the normal range and changes in transfer were measured. These data show that molecules smaller than the limiting size will transfer at an increased rate in response to elevated pressures. Larger molecules did not demonstrate an increased transfer with raised cerebrospinal fluid pressures, suggesting that the pathways did not enlarge.

Characteristic endothelial junctions in different segments of the vascular system

Among the structural features potentially important in the control of the integrity and permeability of the endothelial lining are its intercellular junctions. The points of interest in relation to the endothelial junctions are: their permeability to molecules of different sizes, the extent of cell to cell adhesion, and the existence of intercellular communications. Recent data have shown that alterations in endothelial junctions permeability and integrity may play an important role in inflammation, atherosclerosis as well as in the production of both hemorrhage and thrombosis. The present study was carried out to obtain more information on the fine structural organization of the endothelial junctions in different segments of the vascular system. The identification of small vessels in sectioned tissues is sometimes uncertain and since it could be of considerable importance for structural-functional correlations, we have started to study well defined sequential segments of the microvasculature. Small units consisting of an arteriole, its capillaries and the emerging venule (ACV units) were identified in the rat omentum fixed in situ . Such units were processed for thin sectioning and freeze-fracturing either as a whole or as isolated segments. On ACV units we have examined, so far, the organization of the endothelial junctions. The results showed that the intercellular junctions of the endothelium has continuous and elaborate tight junctions with enclosed large gap junctions (communicating junctions or maculae communicantes). The capillary endothelium is provided with tight junctions formed by staggered strands. The pericytic venules and the muscular venules exhibit loosely organized endothelial junctions with low profile ridges and grooves, usually devoid of particles. No gap (communicating) junctions were found in capillaries and pericytic venules, whereas the muscular venules display small, isolated gap (communicating) junctions. By extending the investigation to the large vessels, we found out that the endothelium of arteries and aorta exhibits a variable combination of well organized tight junctions and gap (communicating) junctions, whereas in the venous part of the circulation (veins, vena cava) there are less elaborate tight junctions and the gap (communicating) junctions are in low frequency. The loose venular junctions may explain low local resistance to stress and correlated increased permeability.

Partial molar volumes of As, Sb, Bi and Sn bromides in some non-polar organic solvents

Partial molar volumes, V 2 , of arsenic, antimony, bismuth and stannic bromides have been computed in benzene, cyclohexane, carbon tetrachloride and p-dioxane from the experimental density data at 303·15 and 313·15°K. For stannic bromide the results obtained are in good agreement with those predicted by Hildbrand's Regular solution model whereas for the other bromides the regular solution model yields higher V 2 values. The difference between the entropy of solution, S 2 − S 2 S , determined from the change of solubility with temperature and the ideal value can be attributed to: (i) the entropy of expansion on mixing, (ii) the entropy of mixing of molecules of different size at constant volume, and (iii) the specific solute-solvent interactions resulting in the formation of stable complexes.

The second and the third virial coefficients of athermal polymer solutions

The second and the third virial coefficients in the lattice model of athermal mixtures of molecules of different sizes are calculated. All computations have been done for two- and three-dimensional simple square and simple cubic lattices.