Identification and partial characterization of a new (50 S) subviral particle in Mengo virus-infected L cells.

A previously undetected subviral particle has been found in Mengo virus-infected L cells by sucrose density gradient centrifugal analysis of cytoplasmic supernatants (S₂₀) prepared from cells after labeling with [³H]amino acids during the early to mid-log phase of virus production. The particle (designated the “50 S particle” from its position between the ribosomal subunits in the gradient), together with mature virions (150 S) and previously described 14 S particles (McGregor et al., 1975), can be recovered from the S₂₀ fraction by high-speed centrifugation. It contains no RNA and is composed of equimolar amounts of the polypeptides ?, α, and γ. The results of conventional pulse-chase experiments suggest that it may be a precursor in the assembly of Mengo virions, but more convincing evidence that this is the case was obtained from experiments in which the chase was carried out in the presence of cordycepin (3′-deoxyadenosine). In the presence of this inhibitor of viral RNA synthesis, there is a significant accumulation of 50 S particles, and when the inhibition in reversed, a quantitative transfer of radiolabel from 50 S particles to mature virions ensues. The recovery of 50 S particles (and of mature virions) from cell homogenates is strongly dependent upon the concentration of KCl in the suspending buffer; only trace amounts are recovered at concentrations of less than 60 mM, while maximum recovery is achieved at a concentration of 100 mM.     

Stability and immunogenicity of empty particles of foot-and-mouth disease virus

Summary Three strains of foot-and-mouth disease virus were shown to contain significant amounts of naturally occurring 75 S, empty particles as well as the infectious, 140 S full particles. One of these strains — A Pando (1970) — was studied in detail.The empty particles from this virus strain were shown to have an observed sedimentation coefficient of 67S in 0.04m phosphate buffer; they were labile in SDS, non-infectious and probably RNA-free and, on heating, they broke down to 12 S subunits as did the 140 S particles. The empty particles differed from the full particles in their polypeptide composition since they contained VP₀, but there was no evidence for a diminished content of VP₄.The 75 S particles were shown to be present in significant amounts and to be stable to AEI inactivation. At 4° C they were stable for at least two years. In guinea pigs they were as immunogenic as the 140 S particles. The antisera raised against the 75 S particles had the same serological specificity in neutralization tests as sera prepared against the 140 S particle. It was concluded that the 75 S particles from the A Pando (1970) strain of FMD virus may provide as important a contribution as 140 S particles to the immunogenicity of inactivated vaccines prepared from this virus strain.With 5 Figures     

The synthesis of a particle-forming cellular protein is enhanced by Mengo virus infection

We have detected a cellular protein which not only escapes the shutoff of host translation induced by Mengo virus, but is synthesized in increasing amounts during Mengo virus infection. The protein has an apparent molecular weight of 20,000 and is contained in a remarkably stable cytoplasmic particle with a sedimentation coefficient of approximately 16 S in sucrose gradients. In the electron microscope this particle appears as a sphere of approximately 12 nm diameter. The synthesis of the protein is stimulated in mouse L cells and in HeLa cells infected with Mengo virus. Its synthesis cannot be induced, however, by stress (heat) or by infection with reovirus.     

Structure of the mengo virion. VI. Spatial relationships of the capsid polypeptides as determined by chemical cross-linking analyses.

The asymmetric structure unit of the Mengo virus capsid comprises one molecule each of the polypeptides α, β, and γ. Structure units are clustered in pentamers which are centered at each of the 12 vertices of a T = 1 icosahedral lattice (Mak et al., 1974). The location of the ～-60 δ polypeptides in the capsid has not been established. In order to obtain information about the arrangement of α, β, and γ in the structure unit and to determine which polypeptides participate in the noncovalent interactions responsible for pentamer formation and capsid stabilization, virions were reacted with bifunctional crosslinking reagents and the polypeptide complexes produced were identified by gel electrophoresis. Using the reversible crosslinkers dimethylsuberimidate (DMS) and dithiobis(succinimidyl propionate) (DSP), positive identification of βγ, αγ, αβγ, α₂, α₃, and α₄ complexes was made. Complexes involving S were not detected, nor were β_n or γ_n. The latter observation indicated that the hydrophobic interactions among αβψ structure units in a pentamer involve α-α contacts. When virions crosslinked with DMS, DSP, or dimethyladipimate (DMA) were subsequently dissociated by 0.1 M NaCl at pH 6 and examined in the electron microscope, it was shown that only treatment with DSP prevented complete capsid dissociation. Since DSP crosslinking alone produced αβ complexes, it was concluded that the interactions between adjacent pentamers probably result from α-β contacts. Treatment of Mengo virions with formaldehyde produced crosslinks between β and γ polypeptides and the RNA. Based upon these data, a model for the organization of individual polypeptide species within the Mengo virus capsid is presented.     

Mutants of sindbis virus II. Characterization of a maturation-defective mutant, ts103

Mutant ts103 is a minute-plaque former which grows very slowly at any temperature and produces, under optimal conditions, virus yields of 3–10% of those of the parental HR strain. It is slightly temperature sensitive with growth. It reverts at a frequency of 10^?7 to 10^?8 to large-plaque, temperature-independent strains and thus is possibly two mutations removed from the large-plaque HR strain of Sindbis virus. The very slow rate of virus production by ts103 appears to be due to a defect in the final stages of virus maturation, the budding of nucleocapsids through the plasma membrane to produce infectious virus. RNA synthesis after infection by the mutant appears to be normal. Nucleocapsids are produced in ts103-infected cells in amounts comparable to that produced in HR-infected cells, although a significant fraction of the mutant nucleocapsids sediment more slowly than HR capsids. Viral hemagglutinin appears in the cell surface earlier in ts103 infection than in HR infection. Electron microscopy of cells infected by ts103 reveals the presence of large amounts of nucleocapsids apparently in the process of budding. Yet the release of mature virus is delayed and the final yield of virus is much reduced in ts103 infection. Furthermore, ts103 budding occurs almost exclusively in virus-specific processes which are quite different in appearance from those found after infection by other strains of Sindbis virus. The virus-like particles produced during infection of chick embryo fibroblasts by this mutant have been examined by sedimentation velocity, isopycnic centrifugation, thermal inactivation at 56°, acrylamide-gel electrophoresis of viral RNA and viral protein, and electron microscopy. Some particles are produced during ts103 infection, which cosediment with Sindbis HR virus at 280 S, and are indistinguishable from HR by a number of other criteria, including isopycnic density, protein composition, sedimentation coefficient of the nucleocapsid, size of RNA, and specific infectivity. However, these 280 S ts103 particles are more sensitive to thermal inactivation at 56° than HR virions. Most of the virus-specific particles produced during ts103 infection sediment faster than 280 S and are heterogeneous in structure. These particles contain more than one nucleocapsid in a single envelope, and the tightness of packing of the nucleocapsids in the envelope is different from particle to particle. This leads to variability in isopycnic density, with particles denser or less dense than HR virus, as well as particles of HR density. In addition, this pleomorphism means that particles containing the same number of nucleocapsids may differ in sedimentation coefficient. These rapidly sedimenting ts103 particles contain small numbers of the nucleocapsids which sediment more slowly than capsids from HR virus, but most of the nucleocapsids are indistinguishable from those of HR. The protein composition of these multicored particles is very similar to that of the HR strain (as examined by acrylamidegel electrophoresis) although they do appear to contain slightly higher ratios of nucleocapsid protein relative to the glycoproteins. These multicored particles are fully infectious with a specific infectivity approaching 100%. The data are all consistent with the following hypothesis: ts103 has an altered nucleocapsid protein. During budding, ts103 capsids interact less strongly with viral glycoproteins in the cell surface than is the case for HR infection. This weakened binding results in a very slow rate of maturation and the production of a large fraction of multiploid particles. In addition some misassembled capsids arise which are unable to mature into normal-sized virions.     

Regional Distribution of Aerosol Deposition in Rat Lungs Using Magnetic Resonance Imaging

The toxic or therapeutic effect of an inhaled aerosol is highly dependent upon the site and extent of deposition in the lung. A novel MRI-based method was used to quantify the spatial distribution of particles in the rat lung. Rats were exposed to 0.95 μm-diameter iron oxide particles in a controlled manner (N = 6) or to particle-free air (N = 6). Lungs were fixed in 3% glutaraldehyde by vascular perfusion, excised and imaged in a 3T scanner using a gradient-echo imaging protocol. The signal decay rate, $R_{2}^{\ast}$ , was measured in each voxel of the entire left lung (1 mm thick slices). $R_{2}^{\ast}$ was significantly higher in exposed animals (0.0065  ±  0.0006 ms^?1) than in controls (0.0050  ±  0.0003 ms^?1, p < 0.001). A calibration curve between $R_{2}^{\ast}$ and concentration of deposited particles (C _part) was obtained by imaging gel samples with known particle concentrations. Regional deposition was assessed by comparing C _part between the outer (C _{part,peripheral}) and inner (C _part,central) areas on each transaxial slice, and expressed as the $\frac{c}{p}$ ratio. C _{part,peripheral} (1.54  ±  0.70 μg/mL) was significantly higher than C _part,central (1.00  ±  0.39 μg/mL, p<0.05), resulting in a $\frac{c}{p}$ ratio of 0.65. This method may be used in future studies to quantify spatial distribution of deposited particles in healthy and diseased lungs.     

Purification and properties of tomato spotted wilt virus

Tomato spotted wilt virus was purified by chromatography on columns of calcium phosphate, precipitation with polyethylene glycol, density gradient centrifugation, and ascending zone electrophoresis in a sucrose density gradient. Examination of the virus by electron microscopy revealed particles of different shapes in different suspending media. Particles fixed with glutaraldehyde were spherical and somewhat flattened and had a corrected diameter of 85 nm.Antisera with a titer of $\text{1}\text{128}$ against the virus were prepared which did not react with plant antigens.The virus had a sedimentation coefficient s_20,w of 530 S and, when fixed in 0.5% glutaraldehyde, it had an electrophoretic mobility at pH 7 of ?19.8 × 10^-5 cm² V^?1 sec^?1.     

Structure of the Mengo virion. II. Physicochemical and electron microscopic analysis of degraded virus

Incubation of Mengo encephalomyelitis virus at slightly acidic pH in the presence of chloride or bromide ions results in the dissociation of the viral capsid into uniform protein subunits (13.4 S) with the release of the intact viral genome (Mak et al., 1970). Electron microscopic studies have shown that the 13.4 S subunit has a well defined, slightly ellipsoidal shape, with surface dimensions of 16.8 ± 0.3 × 14.2 ± 0.2 nm. It is concluded from these studies that the virus capsid is composed of 12 of these subunits, arranged in icosahedral symmetry. The 13.4 S subunits can be further dissociated into 4.7 S fragments by incubation in 2 M urea. The 4.7 S fragment has an approximately spherical shape, with a diameter of 6.8 ± 0.3 nm; and has the same polypeptide composition as does the 13.4 S subunit. These observations suggest that there are 5 such fragments in each 13.4 S subunit, for a total of 60 in the complete virus capsid.A model is proposed for the architecture of the Mengo virus particle, based on the physicochemical and electron microscopic data obtained for the intact virion and its dissociation products.     

Influence of individual energy cost on running capacity in warm, humid environments

Purpose

Challenging environmental conditions including heat and humidity are associated with particular risks to the health of runners and triathletes during prolonged events. The heat production of a runner is the product of its energy cost of running (C _r) by its velocity. Since C _r varies greatly among humans, those individuals with high C _r are more exposed to heat stress in warm and humid conditions. Although risk factor awareness is crucial to the prevention of heat stroke and potential fatalities associated therewith, how C _r affects the highest sustainable velocity (V) at which maximal heat loss matches heat production has not been quantified to date.

Methods

Here, we computed in virtual runners weighting 45–75 kg, the influence of C _r variability from 3.8 to 4.4 J·m^?1·kg^?1 on V. Heat loss by radiation, convection, and conduction was assessed from known equations including body dimensions, running velocity (3.4–6.2 m·s^?1), air temperature (T _a, 10–35 °C) and relative humidity (r _h, 50, 70 and 90 %).

Results

We demonstrated a marked and almost linear influence of C _r on V in hot and humid conditions: +0.1 J·kg^?1·m^?1 in C _r corresponded to ?4 % in V. For instance, in conditions 25 °C r _h 70 %, 65-kg runners with low C _r could sustain a running speed of 5.7 m·s^?1 as compared to only 4.3 m·s^?1 in runners with high C _r, which is huge.

Conclusion

We conclude that prior knowledge of individual C _r in athletes exposed to somewhat warm and humid environments during prolonged running is one obvious recommendation for minimizing heat illness risk.     

Further studies on Chara corallina virus

The particles of Chara corallina virus (CCV) and those of tobamoviruses share many properties, but differ in some. CCV particles are tubular, 532 nm long, and 18 nm wide, and are helically constructed with a basic pitch of 2.75 nm; their isoelectric point is pH 3.4–3.7; their sedimentation coefficient (s₂₀, w) is 230 S; they contain 5% RNA with a molecular weight of 3.6 × 10⁶ daltons, and with a base ratio of G 24.5, A 28.0, C 20.0, U 27.5; their coat protein is similar in size to that of tobamoviruses (about 17.5 × 10³ daltons). CCV is considered to be a tobamovirus. CCV may be transmitted experimentally to uninfected Chara corallina cells by injection of virus particles, and causes chlorosis and death in about 10–12 days. A classification of CCV and 68 other tobamovirus isolates, whose coat protein composition is known, showed that CCV is distant from all, but is most closely related to the cucurbit tobamoviruses.     

Accuracy of pulse oximetry during intense exercise under severe hypoxic conditions

There is a growing need to measure arterial oxygen saturation with a non-invasive method during heavy exercise under severe hypoxic conditions. Although the accuracy of pulse oximetry has been challenged by several authors, it has not been done under extreme conditions. The purpose of this study was to evaluate the accuracy of a pulse oximeter (Satlite, Datex, Finland) during exercise under hypoxic conditions where arterial oxygen saturation was below 75%, simulating exercise at extreme altitude. Ten healthy non-smoking men performed two exercise studies of 30?min under normoxia and under hypoxia on two consecutive days. The exercise intensity was 80% of maximal O₂ consumption of O_2max. Arterial oxygen saturation measured by pulse oximetry was corrected (S _pO_2[corr]) according to previously published equations and was compared to arterial oxygen saturation (S _aO₂) in blood samples taken simultaneously from the radial artery. Reference arterial saturation values ranged from 57.2 to 97.6% for the whole data set. This data set was split according to low (S _aO₂?≤?75%) and high (S _aO₂?>?75%) S _aO₂ values. The error of pulse oximetry (S _pO_2[corr]? S _aO₂) was 2.05 (0.87)% [mean (SD)] and 1.80 (1.81)% for high and low S _aO₂ values, respectively. S _pO_2[corr] and S _aO₂ were highly correlated (r?=?0.93, SEE?=?1.8) for low values. During high-intensity constant workload under severe hypoxic conditions, once corrected, pulse oximetry provides an estimate of S _aO₂ with a mean error of 2%. Thus, the correction previously described for S _pO₂ values above 75% saturation applies also to S _pO₂ values in the range of 57–75% during exercise under hypoxic conditions.     

Diversity of Staphylococcus Species Strains Based on Partial kat (Catalase) Gene Sequences and Design of a PCR-Restriction Fragment Length Polymorphism Assay for Identification and Differentiation of Coagulase-Positive Species (S. aureus,S. delphini,S. hyicus,S. intermedius,S. pseudintermedius,and S. schleiferi subsp. coagulans)

A set of degenerate PCR primers was designed and used to amplify and sequence about 75% of the catalase (kat) gene from each of 49 staphylococcal strains. In some strains of Staphylococcus xylosus, S. saprophyticus, and S. equorum, two catalase genes, katA and katB, were found. A phylogenetic tree was generated and showed diversities among 66 partial (about 900-bp) staphylococcal kat nucleotide sequences (including 17 sequences found in GenBank) representing 26 different species. The topology of this tree showed a distribution of staphylococcal species similar, but not identical, to those reported previously based on 16S rRNA, hsp60, sodA, rpoB, tuf, and gap genes. The kat gene sequences were less conserved than those of 16S rRNA, rpoB, hsp60, and tuf genes and slightly more conserved than those of the gap gene. Therefore, kat gene sequence analysis may provide an additional marker for inferring phylogenetic relationships of staphylococci. Moreover, the discrete nucleotide polymorphism revealed in this gene could be exploited for rapid, low-cost identification of staphylococcal species through PCR-restriction fragment length polymorphism (RFLP) analysis. In this study, a PCR-RFLP assay performed by using only the TaqI restriction enzyme was successfully developed for rapid unequivocal identification/differentiation, at species and subspecies levels, of coagulase-positive staphylococci (CPS). The assay was validated by testing the DNA from 100 staphylococcal strains, including reference and wild CPS strains isolated from different environments. This reliable, rapid, and low-cost approach (requiring about 6 h from DNA isolation to the achievement of results and <5 Euros for each strain tested) allowed unambiguous identification of all the strains assayed, including the newly described S. delphini and S. pseudintermedius CPS species.Staphylococci are a group of microorganisms occurring widely in nature. As reported in the List of Prokaryotic Names with Standing in Nomenclature (www.bacterio.net) as of the full update in March 2006, the Staphylococcus genus includes 39 valid species, 11 of which are divided into two or more subspecies, resulting in more than 50 recognized systematic entities (15).The genus includes both human and animal pathogens, generally coagulase-positive staphylococci (CPS) such as S. aureus, S. intermedius, S. delphini, S. hyicus, S. schleiferi subsp. coagulans, and S. pseudintermedius (12, 21, 29, 35), and coagulase-negative staphylococci (CNS) such as S. equorum, S. xylosus, S. carnosus, S. simulans, S. saprophyticus, S. succinus, S. warneri, S. vitulinus, S. pasteuri, S. epidermidis, and S. lentus.Notwithstanding their valuable role in food fermentation (5-9, 23, 24), some CNS such as S. saprophyticus, S. epidermidis, and S. haemolyticus exhibit increasing abilities as opportunistic/emerging pathogens in colonizing animal and human tissues, due in part to the ability of these species (particularly S. epidermidis) to form protective biofilms and their ubiquitous occurrence in the environment (37). Finally, the occurrence of some pathogenic species (S. aureus, S. intermedius, and S. hyicus) in food is a potential public health hazard, since many strains can produce enterotoxins (4, 9, 31). Indeed, enterotoxin-producing food-associated CNS strains (S. carnosus, S. equorum, S. piscifermentans, and S. xylosus) were also recently described by Zell et al. (40). Despite the importance of accurate identification of staphylococcal species by microbiological laboratories, previous studies demonstrated the unreliability of phenotypic methods, including the Vitek 2 system (bioMérieux, Marcy l''Etoile, France), compared to different molecular techniques (5-8, 11) to identify staphylococci.Due to the high sensitivity and specificity they provide, molecular markers are an alternative tool for accurate identification and classification of Staphylococcus species. Evaluations of 16S to 23S rRNA gene polymorphisms by PCR and PCR-denaturing gradient gel electrophoresis (DGGE) analyses of 16S ribosomal sequences have been assessed for the ability to achieve clear identification of strains within the Staphylococcus genus (6). Molecular assays targeting some housekeeping genes such as hsp60 (17), the 16S rRNA gene (14, 18), femA (36), tuf (22), gap (38, 39), sodA (26), rpoB (13), and dnaJ (20, 30) have been used for reliably identifying and classifying staphylococci. However, except for the sodA, hsp60, and nuc gene sequence analyses carried out by Sasaki et al. (29), which allowed some phenotypically identified S. intermedius strains to be reclassified as S. delphini and S. pseudintermedius, to our knowledge, no method allowing rapid identification and differentiation of CPS species including the recently described S. delphini and S. pseudintermedius is available to date.In this study, we evaluated the catalase (kat) gene as a new target for phylogenetic analysis of staphylococci. Catalase is a heme-containing enzyme involved in dismutation of hydrogen peroxide generated during cellular metabolism to water and molecular oxygen. In S. aureus, a correlation between catalase activity and virulence has been observed, suggesting a role for catalase in defensive mechanisms against the oxygen radicals produced by macrophages (28). Additionally, a recent study (25) showed that the S. aureus catalase is a major factor in S. aureus defense against Streptococcus pneumoniae due to neutralization of secreted H₂O₂ produced by the latter microorganism. Sanz et al. (28) showed that catalase deficiency in S. aureus subsp. anaerobius is associated with natural loss-of-function mutations within the structural gene. Therefore, catalase-negative staphylococcal strains may also harbor the catalase gene. Barrière et al. (3) described the katA gene of S. xylosus C2a and supposed the presence of a second catalase gene (katB) in this strain. In fact, the katA-deficient mutant of S. xylosus constructed by these authors still exhibited catalase activity. After analysis of polymorphism within the kat genes of 26 different staphylococcal species, we designed and successfully applied a molecular assay allowing rapid and unequivocal identification and differentiation of CPS species and subspecies.     

A 5-min running field test as a measurement of maximal aerobic velocity

Based on a theoretical approach from world record running data, we have previously calculated that the most suitable duration for measuring maximal aero-bic velocity (v _amax) by a field test was 5 min (v _amax(5)). The aim of this study was, therefore, to check this hypothesis on 48 men of various levels of physical fitness by comparing (v _max(5)) with (v _amax) determined at the last step of a progressive treadmill exercise test when the subject felt exhausted (v _amax(t)) and during a test on a running track, behind a cyclist (following an established protocol) (v _amax(c)). For each test, ( O_2max) was also measured by a direct method on a treadmill ( O_2max(t)) and calculated by an equation for field tests ( O_2max(5) and O_2max(c)). The V _amax(5) [17.1 (SD 2.2) km?·?h^?1] and (v _amax(c)) [(18.2 (SD 2.4) km?·?h^?1] were significantly higher than (v _amx(t)) [16.9 (SD 2.6) km?·?h^?1; P?v _amax(t))?was strongly correlated with (v _amax(5)) (r?=?0.94) and (v _amax(c)) (r?=?0.95) (P?v _amax(5)) and track performances were found in the runners (n?=?9) with experience over a distance of 3,000 m. The O_2max(5) and ( O_2max(c)) were higher than O_2max(t) (+?5.0% and?+?13.7%, respectively; P? O_2max(t) was highly correlated with v _amax(5) (r?=?0.90; P?v _amax and to a lesser degree on O_2max.     

Macromolecular Crystal Engineering Based on Segmented Polymers: Influence of Heteroatoms on the Thermal Properties and Crystallization of m,n‐Polyurethanes Derived from Long‐Chain,Heteroatom‐Containing,Monodisperse α,ω‐Diols

Long‐chain heteroatom‐containing telechelic diols with 29–32 atoms in the backbone were synthesized by a one‐step, free‐radical telomerization of 10‐undecene‐1‐ol with commercially available α,ω‐dithiols. The oxygen and sulfur atoms caused a decrease in the melting point and enthalpy of the diols, compared to the corresponding purely aliphatic diols. The heteroatom‐containing α,ω‐diols HO? (CH₂)₁₁? S? (CH₂)₂? X? (CH₂)₂? S? (CH₂)₁₁? OH, where X = CH₂, O, or O? (CH₂)₂? O, were reacted in the melt with 1,6‐diisocyanatohexane O?C?N? (CH₂)₆? N?C?O, producing a series of polyurethanes containing an increasing amount of heteroatoms. Characterization by differential scanning calorimetry, infra‐red spectroscopy, thermogravimetric analysis, and wide angle x‐ray scattering of the m,n‐polyurethane series showed that, like the telechelic diols they were synthesized from, the heteroatoms caused a decrease in the melting point and enthalpy. However, they did not affect either the decomposition temperature or the crystal structure/packing.

Typical decomposition behavior of all the heteroatom‐containing m,6‐polyurethane.     

Membrane permeability of secondary hydatid cysts of Echinococcus granulosus. Determination of the water diffusional and osmotic permeability coffficients thorugh a syncytial membrane

Diffusional (P_w) and osmotic (P_f) water permeability coefficients were determined for the syncytial epithelium of larval Echinococcus granulosus. P_w was calculated from simultaneous influx measurements of tritiated water and $\text{n-[}{}^{14}\text{C}\text{]}\text{butanol}$ through the hydatid cyst wall. The total diffusional water permeability coefficient, P′_w, was found to be 2.2 × 10^?4cms^?1; which is similar to that previously reported by Rotunno et al. (1974, J. Parasitol. 60, 13–620). Nevertheless, when P′_f is corrected for the unstirred water layer effects, a P_w value of 6.2 × 10^?4cms^?1 is obtained. Thus, the unstirred water layer effects have a very important contribution to P′_w.Total steady state osmotic permeability coefficient, P′_f, was bound to be about 15 × 10^?4 cm s^?1 and it is scarcely affected by those mechanisms that tend to distort the evaluation of P_f. The experimentally determined osmotic coefficient differs from the corrected P_f by only 6%. The P_f/P_w ratio was found to be 2.4.The present study clearly confirms that syncytial membranes can be highly permeable to water, in spite of the fact that they lack tight junctions. Thus, water permeability through epithelial syncytium must be exclusively controlled by the permeability of the apical and/or basocellular membranes.     

Properties of Azotobacter phage PAV-1 and its DNA

Some properties of a phage, PAV-1, that infects both Azotobacter vinelandii strains O and OP have been examined. It contains linear, double-stranded DNA that has a molecular weight of 29 × 106, a sedimentation coefficient, s20,w,Na+0, of 33.8 S and a buoyant density in CsCl of 1.716. The phage appears in electron micrographs to be icosahedral with a short tail surrounded by tail fibers. The virion is calculated to have a weight of about 74 × 106. PAV-1 is unrelated serologically to the Azotobacter phages A14, A21, A31, and A41.     

Terpolymérisation acrylonitrile-styrène-acrylate de méthyle, 4. Copolymérisation en emulsion styrène-acrylate de méthyle en réacteur fermé (batch) en présence de persulfate de potassium

To improve the knowledge of emulsion copolymerization of monomers both swelling their copolymers, but which are of quite different polarity (water solubility), a series of styrene (S)/methyl acrylate (MeA) copolymerizations was carried out in batch at 50°C with potassium persulfate as initiator. The overall rates of copolymerization increase with the amount of MeA in the monomer feed. Copolymer composition follows the usual copolymerization equation if bulk/solution reactivity ratios (r_ij) and monomer partition between aqueous and organic phase are taken into account (simulation). However, accurate kinetic data at low conversion (gas chromatography) put in evidence an enhanced polymerization of the more hydrophilic monomer (MeA), which can be attributed to polymerization in the water phase. Particle sizes increase with conversion and tend to a limiting value, the higher the MeA content is. Particle number (N_p), which is practically constant with conversion of S homopolymerization, tends to increase with MeA content as polymerization proceeds. This trend is enhanced if the emulsifier (sodium dodecanesulfonate, SDS) concentration is increased. Overall propagation rate constants were estimated as function of the experimental conditions and monomer concentration within the particles. From kinetic data (rate of polymerization) and N_p, it was found that the average number of radicals per particle, ñ, remains close to 0,5. It was then possible considering S(k_p = 125 1 · mol^?1 · s^?1) as a standard monomer, to estimate the polymerization rate constant for MeA (335 1 · mol^?1 · s^?1). Since adsorption of emulsifier was shown to be closely related to particle surface composition, the specific area A_s of SDS was measured on latices at various conversions and initial monomer feeds. As conversions increases, the particle surface appears to be richer and richer in MeA, which corresponds to a particle structuration. Strong and weak acid group titration is also in quite good agreement with the colloidal behaviour.     

Modification of electrophysiological and pharmacological properties of K channels in neuroblastoma cells induced by the oxidant chloramine-T

The effects of chloramine-T (CL-T) on voltage-dependent potassium channels in neuroblastoma cells were analysed using the whole-cell current recording technique. CL-T irreversibly decreased the peak whole — cell K current, considerably slowed its inactivation and shifted its activation-voltage curve towards positive voltages by 6 mV. Under control conditions, the inactivation of the whole-cell K current could be described by the sum of two exponentials, F and S, whose time constants at +50 mV were _F=1.00±0.15 s and _S=5.72±0.47 s respectively. After CL-T, it could be described by the sum of two (S₁ and S₂) or three (F, S₁ and S₂) exponentials whose time constants at +50 mV were: _F=0.81±0.22 s, _S1=6.46±0.60 s and _S2=48.56±3.64 s. Under control conditions, F and S inactivating components of the whole-cell K current were blocked by 4-aminopyridine, with a Hill coefficient of 1 and apparent dissociation constants of 0.04 and 0.7 mM respectively. After CL-T, both S₁ and S₂ components were equally blocked by 4-aminopyridine with a Hill coefficient of 0.25, being reduced to 64% of their control values by 10 mM. CL-T is known to slow the inactivation of sodium channels and to oxidize sulphydryl amino acids and unsaturated lipids. It is concluded that the inactivation gates of voltage-dependent sodium and potassium channels are either constituted of the same amino acid residues or are controlled by unsaturated lipids surrounding or bound to the channel proteins.     

Screening and appraisal for immunological adjuvant-active fractions from Platycodon grandiflorum total saponins

In this study, the total saponins from the root of Platycodon grandiflorum (PGS_t) was subjected to D101 macroreticular resin column chromatography to afford four fractions (PGS₃₀, PGS₅₀, PGS₇₅ and PGS₉₅). PGS_t and its four fractions were evaluated and compared for the haemolytic activities and adjuvant potentials on the specific cellular and humoral immune responses of ICR mice against recombinant hepatitis B surface antigen (HBsAg). PGS_t, PGS₃₀, PGS₅₀, PGS₇₅, and PGS₇₅ showed a slight haemolytic effect, with their concentration inducing 50% of the maximum haemolysis (HD₅₀) being 16.13?±?0.81, >200, 17.53?±?0.24, 20.16?±?0.76, 76.31?±?2.20?μg/mL against 0.5% rabbit red blood cell, respectively. PGS_t, PGS₅₀, and PGS₇₅ significantly not only enhanced the Con A-, lipopolysaccharide-, and HBsAg-induced splenocyte proliferation, but promoted the killing activities of natural killer (NK) cells from splenocytes in HBsAg-immunized mice (P?<?0.01 or P?<?0.001). HBsAg-specific IgG, IgG1, IgG2a, and IgG2b antibody levels in serum were also significantly enhanced by PGS_t, PGS₅₀, and PGS₇₅ compared with HBsAg control group (P?<?0.05, P?<?0.01, or P?<?0.001). Moreover, the adjuvant effects of PGS₅₀ and PGS₇₅ on the cellular immune responses and HBsAg-specific IgG2a and IgG2b antibody responses were more significant than those of Alum, PGS₃₀, and PGS₉₅. The results indicated that PGS₅₀ and PGS₇₅ could improve both cellular and humoral immune responses, and elicit a balanced Th1/Th2 response to HBsAg in mice, and that PGS₇₅ may be developed as an ideal candidate adjuvant for hepatitis B vaccine.     

Inability of the nondefective Rous sarcoma provirus to generate, upon transfection, a transformation-defective virus.

A cyanophage which infects the unicellular blue-green algae A. nidulans and S. cedrorum has been isolated from a waste stabilization pond. It is serologically related to another phage (AS-1) that infects these hosts, and has consequently been named AS-1M. The phage is morphologically identical to AS-1, and consists of an hexagonal head with edge-to-edge diameter of 900 Å, and a long contractile tail measuring 2400 by 220 Å. The phage has a sedimentation coefficient of 754 S and a buoyant density in CsCl of 1.490 g/ml. The DNA is double-stranded and has a contour length of 29.5 μm and an S^o_20,w of 45.6 ± 0.9 S. These values indicate a molecular weight of the DNA of 57 ± 3 × 10⁶. The buoyant density of the DNA is 1.714 g/ml in CsCl, suggesting a GC content of 55%. Thermal denaturation of the DNA yields a T_m of 74°, which implies a slightly lower GC content of 52%.