Dusty plasma in the region of the lunar terminator

Dusty plasma in the region of the lunar terminator is considered. It is shown that, in this region, a structure resembling a plasma sheath forms near the lunar surface. This sheath creates a potential barrier, due to which electrons over the illuminated part of the Moon are confined by electrostatic forces. The width of the sheath-like structure is on the order of the ion Debye length. In this structure, significant (about several hundred V/m) electric fields arise, which lift charged micron-size dust grains to heights of several tens of centimeters. The suggested effect may be used to explain the glow observed by the Surveyor spacecraft over the lunar terminator.     

An expression for the rate of return of an egg after artificial deformation

The forces which may be involved in the restoration of a deformed cell to its normal shape are considered. Estimates of the order of magnitude of the forces suggest that the most important forces are those due to surface tension, membrane elasticity and viscosity. An approximate expression is then derived for the rate of return of an elongated or compressed egg. The former expression is compared with data on eggs ofArbacia by E. N. Harvey and H. Shapiro, and it is found to agree sufficiently well with the data. The initial surface force is too low compared with that given by K. S. Cole but various factors are discussed which could contribute to this discrepancy. The value for the net viscosity of the egg is about twice the value arrived at by L. V. Heilbrunn for the egg protoplasm.     

On the mechanics of viscous bodies and elongation in ellipsoidal cells

After deriving some auxiliary equations for the average elongation of a viscous body under the action of forces derived from a potential, the diffusion problem for an ellipsoidal cell with a constant rate of reaction is solved for the case of an infinite permeability. The equation of elongation of such a cell under the influence of diffusion forces is derived, and compared with the, approximate expression obtained by N. Rashevsky for any kind of oblong cell. The two equations are in fair agreement. Effects of constant and variable surface tension are studied.     

THE CHANGING PATTERN OF BIREFRINGENCE IN PLASMODIA OF THE SLIME MOLD, PHYSARUM POLYCEPHALUM

Plasmodia of the acellular slime mold, Physarum polycephalum, reveal a complex and changing pattern of birefringence when examined with a sensitive polarizing microscope. Positively birefringent fibrils are found throughout the ectoplasmic region of the plasmodium. In the larger strands they may be oriented parallel to the strand axis, or arranged circularly or spirally along the periphery of endoplasmic channels. Some fibrils exist for only a few minutes, others for a longer period. Some, particularly the circular fibrils, undergo changes in birefringence as they undergo cyclic deformations. In the ramifying strand region and the advancing margin there is a tendency for fibrils of various sizes to become organized into mutually orthogonal arrays. In some plasmodia the channel wall material immediately adjacent to the endoplasm has been found to be birefringent. The sign of endoplasmic birefringence is negative, and its magnitude is apparently constant over the streaming cycle. The pattern of plasmodial birefringence and its changes during the shuttle streaming cycle of Physarum are considered in the light of several models designed to explain either cytoplasmic streaming alone or the entire gamut of plasmodial motions. The results of this and other recent physical studies suggest that both streaming and the various other motions of the plasmodium may very likely be explained in terms of coordinated contractions taking place in the fibrils which are rendered visible in polarized light.     

IgA isotype-restricted idiotypes associated with T15 Id+ PC antibodies

Idiotypes are believed to be due to the structural conformation of the variable region of immunoglobulins (Ig). We have found an idiotype (C3-24) that requires both variable and constant regions of the heavy chain to be expressed. C3-24 Id is associated with both the T15 variable region from anti-phosphorylcholine (PC) antibodies and the constant region for the alpha-heavy chain. High titer anti-PC serum from a variety of inbred strains of different Ig haplotypes failed to express C3-24 Id. However, when IgA but not IgG or IgM fractions were isolated from a pool of anti-PC serum from BALB/c mice, more than 70% of the molecules expressed C3-24 Id. The high frequency of the expression of C3-24 Id in IgA anti-PC hybridoma proteins from mice of different Ig haplotypes and in the IgA fraction of normal anti-PC antibodies from BALB/c and presumably other strains of mice suggests that idiotypic determinants produced by the three-dimensional product of VH and CH regions may not be unusual.     

Cytoplasmic streaming inParamecium

Summary Certain species ofParamecium demonstrate rotational cytoplasmic streaming, in which most cytoplasmic particles and organelles flow along permanent route, in a constant direction. By means of novel methods of immobilization, observation and recording, some dynamic properties of cytoplasmic streaming have been described. It was found that the velocity profiles of coaxial layers of cytoplasm have a (parabolic) paraboidal shape and the mean output of cytoplasm flow in different examined zones of streaming is constant. As the consequence of randomly distributed elementary propulsion units within the cytoplasm, particles, which serve as markers of movement, exhibit movements of a saltatory nature; this form of movement is seen inParamecium streaming only in cases of error due to polarization of the saltating particles. Interaction of actin filaments and myosin is likely to occur under specific conditions in microcompartments of cytoplasm where local solations are generated eventually leading to contractions which might propagate on gelated neighbouring areas. Places of elementary contractions are scattered. Therefore the motile effect appears as streaming. Rotational cytoplasmic streaming inParamecium may serve as a convenient model for the study of the dynamics and function of cytoplasmic motility.     

Mathematical theory of imitative behavior in a social group with finite imitation thresholds

The effect of the introduction of either a constant or a variable threshold into Rashevsky's theory of imitative behavior is considered. It is found that in either case it is possible to have five equilibrium configurations, three of which may be stable.     

On the shape of the erythrocyte

A model is postulated which attributes the distinctive biconcave shape of the human erythrocyte to a balance of forces acting on the membrane. The forces considered are electrostatic forces due to a charge distribution on the membrane, a hydrostatic pressure difference acting across the membrane, and forces arising from a constant tension in the membrane. A numerical study indicates that the postulated model will produce an equilibrium shape which is very similar to the observed shape of the human erythrocyte.     

The effect of [Mg2+] on the Ca2+ dependence of ATPase and tension development of fast skeletal muscle. The role of the Ca2+-specific sites of troponin C

Conflicting reports have appeared concerning the effect of [Mg2+] on muscle activity. Several groups have found that increasing [Mg2+] produces a right-ward shift of the pCa-tension curve, while others have found no effect of [Mg2+] on myofibrillar ATPase activity. The present study is a careful evaluation of the effect of [Mg2+] on myofibrillar ATPase, skinned fiber tension development, TnCDANZ (troponin C (TnC)-labeled with 5-dimethylaminonaphthalene-1-sulfonyl aziridine) fluorescence, and simultaneous TnCDANZ fluorescence and tension development in the same fiber. A small effect of [Mg2+] on both ATPase and tension development was found with an apparent association constant of about 2 X 10(2) M-1. The Ca2+ dependence of TnCDANZ fluorescence was similarly effected by [Mg2+], either alone or when incorporated into TnC-depleted skinned fibers (K'Mg approximately equal to 2-3 X 10(2) M-1), suggesting that the effect of [Mg2+] on activity is due to an effect of [Mg2+] on Ca2+ binding to the Ca2+-specific sites of TnC. It is not yet clear whether this effect of [Mg2+] is through direct competition at the binding sites or through indirect effects. In either case, the calculated effect of physiological [Mg2+] is so small that the regulatory sites of TnC can still be considered "Ca2+-specific." In addition, a slightly greater effect of [Mg2+] on tension development (K'Mg = 4.62 X 10(2) M-1) was observed only for very low levels of [Mg2+], which might suggest an additional effect of Mg2+ on tension development which is saturated by millimolar Mg2+.     

Vectors for the expression of PCR-amplified immunoglobulin variable domains with human constant regions.

Cassette vectors have been constructed for mammalian expression of complete immunoglobulin heavy and light chain genes whose variable regions are produced by the polymerase chain reaction (PCR). The light and heavy chain vectors have promoter, leader, partial intron, enhancer and constant region segments within modified pSV2-gpt and pSV2-neo plasmids, respectively. Variable (V) regions are obtained by PCR using a two step process: 1) the V gene is amplified from genomic or cDNA, cloned into an intermediate vector and sequenced; 2) the first PCR product serves as the template for a second amplification in which restriction enzyme recognition sites and limited flanking intron sequence are added. The second PCR product is inserted into the expression vector, which is then transfected into mouse myeloma cells. These vectors contain human constant regions and may be used to express chimeric, humanized or human Ig genes. This report describes the design of these vectors and their application for the expression of chimeric 60.3, an anti-CD18 antibody.     

Protein folding and association: insights from the interfacial and thermodynamic properties of hydrocarbons.

We demonstrate in this work that the surface tension, water-organic solvent, transfer-free energies and the thermodynamics of melting of linear alkanes provide fundamental insights into the nonpolar driving forces for protein folding and protein binding reactions. We first develop a model for the curvature dependence of the hydrophobic effect and find that the macroscopic concept of interfacial free energy is applicable at the molecular level. Application of a well-known relationship involving surface tension and adhesion energies reveals that dispersion forces play little or no net role in hydrophobic interactions; rather, the standard model of disruption of water structure (entropically driven at 25 degrees C) is correct. The hydrophobic interaction is found, in agreement with the classical picture, to provide a major driving force for protein folding. Analysis of the melting behavior of hydrocarbons reveals that close packing of the protein interior makes only a small free energy contribution to folding because the enthalpic gain resulting from increased dispersion interactions (relative to the liquid) is countered by the freezing of side chain motion. The identical effect should occur in association reactions, which may provide an enormous simplification in the evaluation of binding energies. Protein binding reactions, even between nearly planar or concave/convex interfaces, are found to have effective hydrophobicities considerably smaller than the prediction based on macroscopic surface tension. This is due to the formation of a concave collar region that usually accompanies complex formation. This effect may preclude the formation of complexes between convex surfaces.     

The trajectories of particles suspended in electrolytes under the influence of crossed electric and magnetic fields. Possible explanation of the sensitivity of organism to magnetic fields

We observed that particles, suspended in an electrolyte and brought into crossed magnetic and electric fields of low intensities, will deviate in the central part of the electrophoresis chamber of a standard Zeiss Cytopherometer with a component vertical to both fields. The direction and magnitude, however, were sharply at variance with what would be expected by the action of the Lorentz force (EMF) on the surface of the particles. The magnitude of the deviation depends upon the magnetic and electric field strength, the ion concentration of the suspension medium and the geometry of the chamber. The movement of the particles is due to streaming of the electrolyte which is mainly caused by inhomogeneities of the electric field in the electrophoresis chamber. The magnitude of the effect is high enough to occur physiological conditions. Magneto-electrophoretic streaming might eventually act as a transducer mechanism which could explain the ability of some animals to orientate themselves in the geomagnetic field.     

Transmission of the eect of an antifungal agent within a single hypha

A micro-compartment culture method was devised in which a single hypha of Rhizopus stolonifer growing on an agar section traversed an antifungal non-diffusible barrier to another agar section; thus the local environment of the distal or proximal part of the hypha could be controlled independently. The responses in terms of hyphal extension of the test fungus to local application of amphotericin B in this culture system were estimated by using an automatic analysing system. After hyphae had traversed the barrier, distal application of amphotericin B caused no appreciable effect on the proximal hyphae. In contrast, proximal application of amphotericin B caused inhibition of the extension of distal hyphae. The reversal of polarized cytoplasmic streaming also occured during the inhibition of distal hyphal extension. The extents of inhibition of the distal hyphal extension and the cytoplasmic streaming were dependent upon the hyphal distance between the amphotericin B application site and the hyphal tip. These results show that the effect of an antifungal agent on a hypha depends on the region of the hypha exposed. Cytoplasmic streaming may play key role in the transmission of antifungal effects within a single hypha.     

Estimating the Dilution Effect Due to Unreliability of Dichotomous Outcome Variables From Kappa

If category-specific reliabilities are constant across groups, the difference in group-specific "success" probabilities estimated from an unreliable dichotomous outcome variable can be shown to be diluted. Thus, although an intervention may truly have a sizable effect, this effect may not be detectable because of unreliability of the outcome variable. This article explores the dilution effect in a latent class analysis framework in which reliability is defined as the probability with which the manifest measure and the true state correspond. The size of the dilution effect will be related to the popular kappa coefficient, which is often used to assess the reliability of dichotomous variables. Conditions will be specified under which the magnitude of the dilution effect can be estimated from kappa.     

The endogenous difference in the rates of acropetal and basipetal cytoplasmic streaming inChara rhizoids is enhanced by gravity

Summary Measurements of cytoplasmic streaming inChara rhizoids were made by a streak-photography method combined with dark-field illumination. The velocity of cytoplasmic streaming in the acropetal direction was faster than in the basipetal direction. The difference in the streaming velocities in both morphological directions was apparently due to endogenous forces. In addition to this, a small difference attributable to gravity was superimposed if the rhizoid was oriented parallel to the gravity vector. The difference in the endogenous forces underlying the oppositely directed streams may be as high as about 12-fold the force imposed by gravity but, on average, it is about 5-fold the gravity force. In the normal vertical position of the rhizoid, this endogenously generated difference is enhanced by the gravity effect. In contrast to the variability of streaming rate due to endogenous forces, the effect of the gravity force is relatively uniform. The difference between acropetal and basipetal streaming velocities is perpetuated over the whole range of lowered velocities after treatment with cytochalasin B. After prolonged incubation in cytochalasin B, the basipetal streaming stops earlier than the acropetal streaming. A difference in the length of filaments on both sides of the streaming machinery in rhizoids is proposed as the structural basis for the difference in velocities.     

The trajectories of particles suspended in electrolytes under the influence of crossed electric and magnetic fields

We observed that particles, suspended in an electrolyte and brought into crossed magnetic and electric fields of low intensities, will deviate in the central part of the electrophoresis chamber of a standard Zeiss Cytopherometer with a component vertical to both fields. The direction and magnitude, however, were sharply at variance with what would be expected by the action of the Lorentz force (EMF) on the surface of the particles. The magnitude of the deviation depends upon the magnetic and electric field strength, the ion concentration of the suspension medium and the geometry of the chamber. The movement of the particles is due to streaming of the electrolyte which is mainly caused by inhomogeneities of the electric field in the electrophoresis chamber. The magnitude of the effect is high enough to occur under physiological conditions. Magneto-electrophoretic streaming might eventually act as a transducer mechanism which could explain the ability of some animals to orientate themselves in the geomagnetic field.     

Changes in the structure of lipid bilayer membranes in magnetic fields

In terms of structural voluminous phases the structure of bilayer lipid membranes in the constant magnetic field far from the point of phase transition is examined. The field influence on the area of the membrane black part is due to surface tension of voluminous phases. It is noted that the effect is squared with the field and is negative under gomeotropic orientation of the molecules on the surface. The dependence of the effect on temperature is predicted and its possible mechanisms are examined.     

Isolation, characterization, and recombinant expression of multiple serpins from the cat flea, Ctenocephalides felis

Several clones encoding serine protease inhibitors were isolated from larval and adult flea cDNA expression libraries by immunoscreening and PCR amplification. Each cDNA contained an open reading frame encoding a protein of approximately 45 kDa, which had significant sequence similarity with the serpin family of serine protease inhibitors. The thirteen cDNA clones isolated to date encode serpin proteins, which share a primary structure that includes a nearly identical constant region of about 360 amino acids, followed by a C-terminal variable region of about 40-60 amino acids. The variable C-terminal sequences encode most of the reactive site loop (RSL) and are generated by mutually exclusive alternative exon splicing, which may confer unique protease selectivity to each serpin. Utilization of an alternative exon splicing mechanism has been verified by sequence analysis of a flea serpin genomic clone and adjacent genomic sequences. RNA expression patterns of the cloned genes have been examined by Northern blot analysis using variable region-specific probes. Several putative serpins have been overexpressed using the cDNA clones in Escherichia coli and baculovirus expression systems. Two purified baculovirus-expressed recombinant proteins have N-terminal amino acid sequences identical to the respective purified native mature flea serpins indicating that appropriate N-terminal processing occurred in the virus-infected insect cells.     

Evaluation of novel control elements by construction of eukaryotic expression vectors

A novel mammalian eukaryotic expression vector for the production of immunoglobulin heavy chain (IgH) genes has been designed. This expression vector contains the variable heavy chain (VH) promoter, the IgH intron enhancer (μE) and the IgH 3′ enhancer (3′E). This construct, designated pTIF-1, was stably transfected into the myeloma cell line J558L. A fivefold increase in the expression level of a rearranged IgH gene was observed when using the pTIF-1 vector containing the 3′E compared to an expression vector lacking this enhancer. Interestingly, this positive effect on the expression level of the 3′ enhancer appears to be position independent. The introduction of two recently identified Ig control elements, HS3 and HS4, to the vector cassette did not further elevate the expression level in the cell line tested. The pTIF-1 vector can be used for expression of any antibody specificity, using PCR amplification of the VDJ region of interest. Furthermore, the constant region can easily be exchanged, which further facilitates studies to dissect different effector functions of IgH constant genes.     

Polar auxin transport and auxin-induced elongation in the absence of cytoplasmic streaming

Summary When cytoplasmie streaming in oat and maize coleoptile cells is completely inhibited by cytochalasin B (CB), polar transport of auxin (indole-3-acetic acid) continues at a slightly reduced rate. Therefore, cytoplasmic streaming is not required for polar transport. Auxin induces elongation in CB-inhibited coleoptile and pea stem segments, but elongation rate is reduced about 40% by CB. Therefore, stimulation of cytoplasmic streaming cannot be the means by which auxin promotes cell elongation, but streaming may be beneficial to elongation growth although not essential to it. A more severe inhibition of elongation develops after several hours in CB. With coleoptiles this could be due to inhibition of sugar uptake; in pea tissue it may be due to permeability changes and cytoplasmic degeneration. CB does not disorganize or disorient microfilament bundles when it inhibits streaming in maize, but appears instead to cause hypercondensation of microfilament material.