bluuebunny/crossref_metadata_2025 huggingface dataset:
New, almost electrostatic, temperature anisotropy instability
Authors: Landau Ronald W.
Published: March 2009

A new, purely growing instability has been found for a bi-Maxwellian plasma in a uniform magnetic field. Instability exists for β;11 = 4βnkT11/B2 > O.591 when Tboxhu;= 0, and ions are neglected. The growth rate is near the electron gyro frequency (or v/c the plasma frequency), and the polarization is almost electrostatic for almost perpendicular propagation. The instability is obtainable only from the complete dispersion relation.
The plasma wake of mesosonic conducting bodies. Part 1. An experimental parametric study of ion focusing by the plasma sheath
Authors: Stone Nobie H.
Published: March 2009

An experimental, parametric investigation has been made of the disturbed ion flow field immediately downstream from conducting bodies of spherical and long cylindrical geometries in a collisionless, mesosonic plasma stream. The ion-acoustic Mach number, S, and the normalized test body potential, Φb, were varied, while the test body radii were of the order of a Debye length for all cases. In addition to standard diagnostics, the ion flux intensity, energy and direction were measured with the recently developed differential ion flux probe. These vector measurements provide direct observations of ion streamlines deflected across the wake axis at an angle proportional to sin-1 (|Φb|½/S) and show that some deflected streamlines are bunched together to form converging ion beams which can exist in the near wakes of both test body configurations. The angle of inclination of the converging ion beams depends linerarly on Φb, while the position of their intercept on the wake axis varies with S|Φb|½. The vector flux measurements also provide direct observations of secondary ion trajectory deflexions in the mid-wake region. These features exhibit parametric dependences that are in good agreement with theoretical calculations that include the effects of the test body and space charge potentials.
Coupled nonlinear Schrödinger equations for Langmuir and elecromagnetic waves and extension of their modulational instability domain
Authors: Gupta M. R. , Som B. K. , Dasgupta Brahmananda
Published: March 2009

A pair of coupled nonlinear Schrödinger equations for transverse and longitudinal waves has been derived. The coupling resulting from equalization of group velocities drives the Langmuir waves modulationally unstable for wavelengths shorter than (mi/me)½ λD and also extends the domain of modulational instability of electromagnetic waves when relativistic effects are taken into account. Instability is found to occur also for the perturbation wavenumber domain in which both the uncoupled Langmuir and electromagnetic waves are modulationally stable. This is shown to be caused by resonant four-wave interaction l + t → l′ + t′. The growth rate of the instability is, in general, of the order of but increases to the extent of a factor (c/vth)2 near the resonance Solitary wave solutions are given. Depending on the relative values of the self-modulation and coupling coefficients, the Langmuir or the transverse or both the waves may be localized in space.
Theory of finite-amplitude electron and ion holes
Authors: Bujarbarua S. B. , Schamel H.
Published: March 2009

A complete investigation is presented of the theory of finite-amplitude electron and ion holes which are localized BGK solutions moving near the respective thermal velocities. For their existence, the distribution functions are required to have a minimum in the resonant region.
Stability of Vlasov equilibria. Part 2. One non-ignorable co-ordinate
Authors: Lewis H. Ralph , Seyler Charles E.
Published: March 2009

The solution of the linearized Vlasov equation is given for an arbitrary equilibrium Hamiltonian in which there is only one non-ignorable co-ordinate. The solution written in terms of integrals with respect to time which only extend over the bounce period of an equilibrium orbit in its equivalent one-dimensional potential. A closed-form solution and a solution based on a Fourier expansion are given. Explicit formulae are presented for Cartesian and cylindrical co-ordinates.
Properties of Alfvén solitons in a finite-beta plasma
Authors: Spangler Steven R. , Sheerin James P.
Published: March 2009

The properties of Alfvén solitons are examined (solitons propagating parallel to the magnetic field in a magnetized plasma) in the case when the plasma possesses a finite pressure. Starting from a two-fluid system of equations, the reductive perturbation method is used to derive a derivative nonlinear Schr ödinger equation, which is solved by a pseudo-potential method. An envelope soliton is found which possesses a width –amplitude relationship. The same functional form for the envelope of the magnetic energy density is obtained regardless of the value of the plasma &bgr;.
The ponderomotive force of a high-frequency electromagnetic field in a cold magnetized plasma
Authors: Karpman V. I. , Shagalov A. G.
Published: March 2009

An expression is derived for the ponderomotive force acting in a cold collisionless magnetized plasma in a high-frequency electromagnetic field. Some related topics, such as the magnetic moment and solenoidal currents induced by the HF field are considered. A microscopic approach is used. The results are in complete agreement with the general expression for the ponderomotive force in a liquid medium with frequency dispersion obtained earlier by Washimi & Karpman by means of phenomenological considerations.
Whistler wave propagation in density ducts
Authors: Karpman V. I. , Kaufman R. N.
Published: March 2009

A theory of whistler wave propagation in axially symmetric density ducts is developed. Both density crests and troughs are considered. The duct width is assumed to be large compared with the parallel wave length. All considerations are based on the Maxwell equations. A number of effects that are not included in the ray theory and (or) the Schrödinger-type equations are elucidated. Among them is whistler detrapping from a density crest at ω < ½ωH. An analytical theory of the detrapping is developed and the corresponding wave attenuation rate in the duct is calculated.
Periodic, highly superluminous, nonlinear waves in a cold, unmagnetized plasma
Authors: Clemmow P. C.
Published: March 2009

With respect to the propagation through a cold, unmagnetized, electron plasma of nonlinear, highly superluminous, plane waves of fixed profile, with electric vector in a fixed plane parallel to the direction of propagation, it is known that, in addition to the familiar longitudinal and quasi-transverse waves, there can also be a third periodic wave. The perturbation method by which this third wave has previously been analysed is of restricted validity, and fails to describe how the wave disappears in the approach to the small-amplitude limit, where the longitudinal and transverse waves alone survive.
The plasma dispersion relation near the two–ion hybrid resonance
Authors: Chiu S. C. , Chan V. S. , Hsu J. Y. , Swanson D. G.
Published: March 2009

The dispersion relation of a deuterium –hydrogen plasma is investigated near the ion cyclotron frequency of hydrogen at varying hydrogen temperatures. It is found that at low hydrogen-to-deuterium temperature ratios, only the fast mode and the ion Bernstein mode are coupled around the hybrid layer. Above a certain critical temperature ratio Th< Thc, these two modes become coupled also to a third mode. Around and above Thc, the wave equation is of sixth order rather than of the fourth order previously discussed.
Dispersion relations for ion waves with finite parallel wavelength in plasmas of finite beta
Authors: Brecht Stephen H.
Published: March 2009

Numerical evaluations of the dielectric response functions were performed and plasma dispersion relations computed for the full function where coupling due to finite β and k∥ are maintained. The basic plasma parameters were chosen to represent 2XIIB with variations in temperature. It is found that various branches exchange polarization and differ somewhat from the more ideal dispersion relation such as the shear Alfvén wave.
Nonlinear propagation of ion-acoustic waves and low-frequency electrostatic modes in a dusty plasma
Authors: Mofiz U. A. , Islam Madhabi , Ahmed Zarin
Published: March 2009

Nonlinear propagation of ion-acoustic waves and low-frequency electrostatic modes in a dusty plasma is investigated. The evolution equations of these modes are developed and solved analytically. It is found that for small grain charge usual ion-acoustic solitons may exist in a dusty plasma, but increasing grain charge destroys them and finally they may disappear. The low-frequency electrostatic mode may be localized, forming solitons, which may act as centres of wave scattering in a dusty plasma.
Low-frequency surface acoustic waves in a collisional plasma
Authors: Vladimirov S. V. , Yu M. Y.
Published: March 2009

Ion-acoustic surface waves in a highly collisional plasma are considered. It is shown that the dispersion and damping of these waves differ considerably from those for a weakly collisional plasma.
Variational theory of the cyclotron-emission source distribution from a mode-conversion layer
Authors: Shvets V. F. , Swanson D. G.
Published: March 2009

This paper presents the theory of an inhomogeneous source of cyclotron emission from a three-branch mode-conversion layer in a non-uniformly magnetized plasma. The physical formulation of the problem is based on the generalized Kirchhoff's law that relates, branch by branch, the emission to the absorption. General integral expressions for both absorbed and emitted energy fractions along each wave branch are obtained. A discrete multi-point model of absorbers and emitters is analysed. A variational principle for the integral of the emitted power is formulated.
An analytical method for the investigation of instability of a collisionless plasma in strong magnetic fields
Authors: Zakharov V. U.
Published: March 2009

An analytical method for the investigation of special types of dispersion relations is presented. In particular, analysis of the propagation of small- amplitude hydromagnetic waves in a collisionless plasma in a strong magnetic field leads to such dispersion relations. The fifth-degree dispersion relation corresponding to a particular case is considered. The necessary stability condition for a steady state and conditions for the degeneration of small- amplitude waves are derived. A comparison with other methods for the analysis of similar dispersion relations is also presented.
Excitation of ion-cyclotron waves by a spiralling ion beam in a plasma cylinder
Authors: Sharma S. C. , Tripathi V. K.
Published: March 2009

A helical ion beam propagating through a plasma cylinder drives electrostatic ion-cyclotron waves to instability via cyclotron interaction. Higher harmonics of the beam cyclotron frequency can be generated in this way. The growth rate increases with the harmonic number. The efficiency of beam energy transfer to the wave can be of the order of a few per cent.
Fusion conditions in a finite-thickness gas-puff staged Z-pinch
Authors: Mirza Arshad M. , Khattak N. A. D. , Iqbal M. , Murtaza G.
Published: March 2009

We investigate the implosion of a dense τ-pinch plasma driven by an annular finite-thickness gas-puff Z-pinch. The imploding Z-pinch traps an axial magnetic field Bz, compressing it to large values in an extremely short time. The temporal variation of Bz then induces an azimuthal τ current on the surface of a fibre placed on the axis, with a rise time an order of magnitude shorter than the rise time of the Z-pinch current. Our numerical results demonstrate that, for a thick gas-puff layer, maximum compression occurs before the current peaks.We also find that at peak compression, fuel densities of the order of 1025 cm-3 and temperatures above 10 keV can be achieved on a time scale of the order of 0.1 ns. Thus a Lawson parameter nτ ≈ 1014 s cm-3 for a DT fibre becomes achievable. The snowplough effect in the Z-pinch exercises a stabilization effect on the growth of sausage and Rayleigh—Taylor instabilities. In the limit of a very thin gas-puff layer, previous results are fully recovered.
Electrically gated ionic channels in lipid bilayers
Authors: Ehrenstein Gerald , Lecar Harold
Published: March 2009

The generation of action potentials in nerve and muscle requires cell membranes with steeply voltage-dependent ionic permeabilities. The voltage-dependent, ion-selective pathways responsible for excitation have been characterized for numerous excitable tissues such as nerve axon, muscle, electric organ, algae and epithelia (Aidley, 1971; Hodgkin, 1964; Cole, 1968). The process of activating ionic pathways by some stimulus, such as a change in membrane potential, is called gating.
Structural basis for the specificity of antibody–antigen reactions and structural mechanisms for the diversification of antigen-binding specificities
Authors: Padlan Eduardo A.
Published: March 2009

The ability of an organism to cope with foreign substances (antigens) depends in part on its capacity to synthesize antibodies (immunoglobulins) of the proper binding specificity to recognize and combine with these antigens. In view of the great variety of possible antigens, antibodies, or more specifically their combining sites, display considerable variation and possess structural properties such as to enable them to bind the antigenic determinants. A vast amount of immunoglobulin sequence data has become available and the three-dimensional structures of a number of immunoglobulin fragments have been elucidated. With these results we can now begin to understand the structural aspects of antibody–antigen reactions. The crystallographic results and the sequence data have been reviewed elsewhere (Capra & Kehoe, 1975; Davies, Padlan & Segal 1975a, b; Gally, 1973; Kabat, 1976; Nisonoff, Hopper & Spring, 1975; Poljak, 1975a, b). Here, an attempt is made to interpret these structural data in terms of the structural evolution of the antibody combining site and the structural basis for the specificity of the binding of antibody to antigen. First, the pertinent crystallographic and sequence data will be presented. Next, the structural studies which reveal the complementarity between antibody and ligand will be described. Then, structural mechanisms by which different combining site structures could be generated will be reviewed.
Enzyme engineering and the anatomy of equilibrium technology
Authors: Hedén Carl-Göran
Published: March 2009

To talk about enzyme engineering in a context of global problems might seem easy, because the subject is so dynamic and its ramifications so numerous. One might for instance talk about the industrial use of immobilized enzymes to achieve steroid transformations suitable for large-scale production of drugs reducing fertility, or one could describe the application of the same technique for chopping off side-chains of penicillin and other antibiotics as a first step in the production of new semisynthetic drugs, that certainly have a global impact. Or it would be tempting to review the potential of enzyme engineering for synthesizing physiologically active polypeptides that find use in husbandry or medicine.
Orientation and mobility of molecules in membranes studied by polarized light spectroscopy
Authors: Johansson Lennart B.-Å. , Lindblom Göran
Published: March 2009

Biological membranes are composed of mainly lipids and proteins. The physical properties of the lipids, forming a bilayer structure, are of crucial importance for the living cell, since the plasma membrane is the guardian barrier towards the environment. Thus, the functioning cell needs a highly stable lipid bilayer, which depends on molecular packing and orientation properties of the various membrane components (Wieslanderet al.1980). The spatial arrangement of the membrane proteins incorporated in the lipid matrix plays an essential role for the different chemical processes occurring at or within the membrane. Information about molecular orientation and mobility is therefore necessary for unravelling the functional mechanisms of a biological membrane.
New looks and outlooks on physical enzymology
Authors: Eigen Manfred
Published: March 2009

Our scientific age is characterized by the extension of our dimensions to the extreme. Radiotelescopes are searching for echoes from the depth of the universe, while electronmicroscopes and X-ray diffractometers make the atomic and molecular structure of matter visible.
Modification of specular reflexion and light transmission by biological surface structures
Authors: Bernhard C. G. , Gemne G. , Møller A. R.
Published: March 2009

Biophysicists, who, by definition, apply physical and mathematical principles to their analysis of biological problems for the understanding of the functions of living organisms, are to a great extent concerned with basic characteristics more or less common to all organisms. As pointed out by Griffin (1958) in his book on acoustic orientation, it may well be that ‘this fruitful preoccupation with the universals of protoplasm tends to foster an unduly restricted view of its many intricate potentialities’. The knowledge of the many ways in which animals and plants are adapted for a ‘successful life’ has had a great impact upon the concepts of evolution and natural selection. As a contribution to the proper understanding of these concepts the study of the biophysical principles, by which various geometrically oriented tissues serve different functions, becomes of special interest.
Dynamics of membrane processes
Authors: Katchalsky A. , Spangler R.
Published: March 2009

I. I. In his illuminating book onThe Nature of Thermodynamics, Bridgeman (1941) points out an intrinsic contradiction between the concepts of physical and biological evolution. In his words: ‘The view that the universe is running down into a condition where its entropy and the amount of disorder are as great as possible has had a profound effect on the views of many biologists on the nature of biological phenomena. It springs to the eye, however, that the tendency of living organisms is to organize their surroundings—that is to “produce” order where formerly there was disorder. Life then appears in some way to oppose the otherwise universal drive to disorder. Does it mean that living organisms do, or may violate the second law of thermodynamics?…’
Evolution of chromosomes and viruses, derivation of structure
Authors: Kilkson R.
Published: March 2009

Since the earliest intelligent history man has tried to understand the origin of life. Some remarkable scientific advances have been made. The concept of natural selection is firmly established as the basis of organic evolution. Advances in the genetic mechanism of inheritance have shed light on the processes and levels at which evolutionary changes occur. Evolution is understood to be a dynamic process, and the organisms present at any given time are those best suited to the environment by virtue of the history of their predecessors. But a deeper question arises: how free is evolution? Are the particular biomolecular structures and processes in existence now in any way uniquely predetermined, or are they the result of a sequence of accidental occurrences?
Regulation of immunity at the cellular level
Authors: Wigzell Hans
Published: March 2009

The origin of pluripotentiality of the immune system in an individual constitutes a major challenge for students of immunology. A vast number of different substances can be shown to be antigenic in an individual, such that their introduction will induce antibody synthesis. These antibodies, mostly detected as serum immunoglobulins, are distinguished by their Capacity for specific combination with the inducer, the antigen. As the specificity of the antibody towards a given antigen can be shown to reside within the amino acid sequence of the molecule by unfolding-refolding experiments (Haber, 1964), it is generally accepted that the antigen-combining capacity of an antibody molecule is under genetic control. So far, studies trying to disclose any unique features of immunoglobulin versus other systems of protein production have failed to do so. No commonly accepted theory yet exists to explain how this multiplicity of immunological potentiality is created at the level of DNA and it is considered beyond the scope of this article to try to cover in detail the various attempts to solve this problem. The reader is referred to a recent review (Lennox & Cohn, 1967) for further details on this subject. It is the intention of the author to describe how pluripotentiality of the immune system operates at the cellular level and to describe and discuss in more detail how regulation of the expression of immunological capacity takes place at the single cell level.
The interpretation of tracer fluxes in terms of membrane structure
Authors: Ussing Hans H.
Published: March 2009

Very early in the era of isotopic tracers it became apparent that tracer fluxes did not always come out as one had predicted from classical measurements of transport by osmosis or diffusion. Thus Hevesy, Hofer & Krogh (1935) determined the water permeability of frog skin from osmotic uptake of water as well as from measurements of its permeability to heavy water. They found the first method to give values some 4–5 times higher than the latter. Although this result at first seemed disappointing, it was soon realized that the two types of experiments provided more information about the nature of osmosis through real membranes than had been available before. Thus it was shown that the results might be explained in terms of interaction between water molecules moving in bulk, possibly through pores in the membrane (Ussing, 1952; Koefoed-Johnsen & Ussing, 1953; Andersen & Ussing, 1957).
Microspectrophotometry of visual pigments
Authors: Carlson Stanley D.
Published: March 2009

Visual pigments are embedded in the disc membranes of the outer segments of vertebrate rods and cones and in the microvilli of invertebrate visual cells. The pigment molecule in both is a most fascinating aggregate of known (the ubiquitous II-cisisomer of vitamin A1or A2-aldehyde = retinal1or2; Hubbard & Wald, 1952) covalently bonded to the unknown (a protein termed opsin) (Anderson, Hoffman & Hall, 1971). This conjugated molecule is called rhodopsin or dehydrorhodopsin (porphryopsin) when the prosthetic portion is retinall or 2 respectively. So sensitive is this sterically hindered, bent and twisted molecule to light that absorption of one photon can initiate its isomerization to the alltransform. This conformational change is but one (but the best known) of the factors leading to receptor membrane changes ushering in the visual impulse.
Non-linear transport behaviour in very thin membranes
Authors: Schlögl R.
Published: March 2009

It appears questionable whether the thermodynamics of irreversible processes can be applied formally in a simple way to the transport of matter or energy across very thin membranes such as lipid bilayers. This is because a thin layer probably cannot be described in a strict thermodynamical sense as a continuous phase.
The Lesions Produced by Ultraviolet Light in DNA Containing 5-Bromouracil
Authors: Hutchinson Franklin
Published: March 2009

The compound 5-bromouracil (BrU) may be incorporated into DNA in place of its analog thymine. This review is concerned with the photochemical lesions produced by the action of ultraviolet light on such BrU-DNA, and consequent biological effects of such lesions.
Primary photochemical reactions in chloroplast photosynthesis
Authors: Bearden Alan J. , Malkin Richard
Published: March 2009

Photosynthesis begins with the absorption of light energy and this absorbed energy is transferred to special sites, termed reaction centres. At these sites, the light energy is transformed into chemical products through an oxidation-reduction reaction that generates the primary reactants, an oxidized pigment molecule (P+) and a reduced electron acceptor (A–) (Clayton, 1972). The subsequent reactions of these species in the dark ultimately results in the formation of chemical products required for the fixation of CO2. In this essay we will discuss the nature of the primary reactants generated in the light reactions of chloroplast photosynthesis, stressing recent advances in the identification and characterization of such reactants.
Van der Waals forces in biological systems
Authors: Israelachvili Jacob N.
Published: March 2009

The theory of van der Waals forces has now developed to a stage where it constitutes a powerful tool in theoretical investigations of many biological systems. In this review we shall consider both the theoretical and conceptual aspects of these forces with the emphasis on the way they may be involved in various biological processes.
The biophysics of ligand–receptor interactions
Authors: DeLisi Charles
Published: March 2009

For the cells of an organism to act in the coordinated fashion necessary for complex functioning, they must be able to receive and transmit information. Information transfer is mediated by molecules released by the cells and may be local, as in the case of neurotransmitters, or long range, as in the case of hormones. It is apparent, however, that irrespective of the range of interaction, a cell must be able to distinguish, with a high degree of precision, the signals relevant to it from an enormous flow of background noise.

Molecular recognition at the cell surface is mediated by receptors: cell surface glycoproteins that usually form an integral part of the plasma membrane (see, for example, Cuatrecasas & Greaves, 1978). Typically, receptors bind the ligands they are designed to recognize with affinities of the order of 108M-1, and they translate that interaction into a sequence of signals that ultimately lead to biological activity.
The application of fluorescent probes in membrane studies
Authors: Azzi Angelo
Published: March 2009

Fluorescence has been used in biochemical studies for many years but only recently has the information content and the practical applicability of the fluorescence method been fully realized.

Following the early studies of Newton (1954) and Weber (11954) and after the initial utilization of fluorescent probes by Chance and coworkers (Azziet al.1969) and Tasakiet al.(1968), in the study of membranes, the use of fluorescence to provide structural information at microscopic or molecular levels in biological membranes has become widespread. widespread. The application of the fluorescence technique to biological systems has progressed parallel to the development of a theoretical basis for fluorescence data interpretation and the synthesis of a large number of fluorescent probes, organic molecules having fluorescence characteristics that are dependent on their environment.
A comparison of X-ray small-angle scattering results to crystal structure analysis and other physical techniques in the field of biological macromolecules
Authors: Kratky O. , Pilz I.
Published: March 2009

In principle, there exist two ways to contribute to structure determination of macromolecules by X-ray diffraction: (a) by analysing diffraction data obtained from the crystalline state, and (b) by interpretation of X-ray small-angle scattering from particles in solution.

The brilliant achievements of X-ray crystal-structure analysis of macromolecules, initiated by the works of Perutz on heamoglobin and Kendrew on myoglobin, are well known and it is evident that its detailed elution of secondary, tertiary and quaternary structure cannot be matched by any other means. However, a number of necessary prerequisites for a successful application, as, for example, the availability of well-defined crystals and heavy atom labelled derivatives thereof to surmount the problem of phase determination are not always given.
Immune responses to hapten conjugatesin vitro
Authors: Kontiainen Sirkka , Mäkelä O. , Hurme M.
Published: March 2009

Several functions of the animal body can take place in cell or tissue cultures with almost unreduced efficiency and precision. Functions, where only one cell type is involved, often do so, but also some differentiation steps where interactions between two or more cell types are clearly needed can take place in tissue culture (Saxénet al.1968).

Most immune responses require collaboration between two or more cell types (Claman, Chaperon & Triplett, 1966; Miller & Mitchell, 1968; Feldmann & Nossal 1972c). Some of them can be easily inducedin vitrobut others cannot. Even when antibody responses can be inducedin vitrotheir intensity varies a great deal. With some antigens and under some circumstances a responsein vitrocan be nearly as strong as onein vivo.A crude comparison can be derived from responsesin vitroandin vivoto the same antigen, conjugate of hapten NIP and pneumococcal polysaccharide type III (NIP-SIll, Nakamura, Ray & Mäkelä, 1973).
Energy transfer and dynamical structure
Authors: Eisinger Josef
Published: March 2009

It is only some 50 years ago that biophysicists obtained reliable experimental methods for estimating the molecular weights of biological macromolecules, chiefly as a result of Svedberg's work in developing the ultracentrifuge as an analytical instrument (Svedberg & Pedersen, 1940). Having gained some understanding of the size of proteins, interest soon thereafter turned to the shape and rotational relaxation times of these molecules, and Perrin's work on fluorescence depolarization helped to lay the foundations there (Perrin, 1929). Biophysics had to wait for the development of X-ray spectroscopy of proteins and nucleic acids to provide a picture of the interior structure of biological macromolecules.
Applications of Fluorescence Correlation Spectroscopy
Authors: Webb Watt W.
Published: March 2009

The preceding paper by Douglas Magde has recounted the basic principles of Fluorescence Correlation Spectroscopy (FCS) as originally described (see Magde, Elson & Webb, 1972; Elson & Magde, 1974; Magde, Elson & Webb, 1974 Elson & Webb, 1975; referred to collectively as MEW), and has described the first application to chemical kinetics. In this paper I shall first illustrate the same principles of FCS with a simple graphical demonstration model based on the scheme for application to lateral diffusion in membranes as it was developed in our laboratory by Dr T. J. Herbert; I shall then proceed to discuss some current research in our group organized jointly with Professor E. L. Elson at Cornell.
The power of movement in plants: the role of osmotic machines
Authors: Hill Bruria S. , Findlay Geoffrey P.
Published: March 2009

The apparent and often spectacular movements of animals and insects, movements of the whole organism in relation to its surroundings arising from internally generated forces, have always been, by their very ubiquity, uppermost in our perception of motion in the living world. Movement in plants, generally of one organ in relation to the whole plant, whilst sometimes spectacular, have often in the past been seen as rather esoteric events, amusing perhaps, but of little importance in the general biological scheme of things. However, this is not so; plant movements are quite widespread in occurrence and all are most probably manifestations of a single physiological process, the change in volume of special motor cells. One particular movement, the opening and closing of stomata, which provides a basic control of photosynthesis, is of fundamental importance to the existence of the whole biosphere.
The structure of serum lipoproteins as analysed by X-ray small-angle scattering
Authors: laggner Peter , MÜller Karl W.
Published: March 2009

Serum lipoproteins are the macromolecular lipid–protein complexes, soluble in aqueous environment, which act as transport vehicles for polar and apolar lipids in the bloodstream. The growing multidisciplinary interest in these systems stems on the one hand from the fact that their physiological functions are intimately related to the pathways of lipid metabolism and catabolism, and on the other hand from their macromolecular nature which renders them accessible to a large variety of experimental approaches for the study of the physical and chemical principles of lipid-protein interaction.
Anomalous small angle scattering
Authors: Stuhrmann H. B.
Published: March 2009

Isomorphous replacement methods have been revolutionary in macromolecular structure research. This has been most clearly demonstrated in protein crystallography. Specific binding of heavy atoms to protein molecules in the crystalline state provides the necessary reference for the phase determination of each Bragg reflexion and opens the way to the direct structure determination to atomic resolution from X-ray diffraction.

Are isomorphous replacement methods applicable to the investigation of non-crystalline structures as well? And if so, would there be any reasonable advantage?

An answer has been given by neutron scattering. Macromolecular assemblies of nucleic acids, proteins and lipids are most easily studied in H2O /D2O mixtures, as the scattering density of the solvent can be adjusted to any of the chemically different partial structures (Stuhrmann, 1974).
The spin 3/2 state and quantum spin mixtures in haem proteins
Authors: Maltempo M. M. , Moss T. H.
Published: March 2009

The magnetic state of iron in haem proteins has long been recognized as a convenient indicator of chemical coordination as well as more subtle biochemical properties. In the trivalent case in particular, there are three magnetically distinct configurations of the five 3delectrons, yielding spin states ofS= 1/2, 3/2 and 5/2. The first and third are extremely familiar, and often lie close enough in energy so that athermalmixture of low-spinS= 1/2 and high-spinS= 5/2 states exists in an ensemble of molecules. Selection rules for common perturbations (ΔS= ∘, ± 1 for the spin-orbit interaction and ΔS= ∘ for the electronic Zeeman interaction) ensure thatquantummixtures, in which the wave function is a true combination ofS= 1/2 andS= 5/2 components, are not observed. The mid-spin,S= 3/2, state, and allowed 5/2–3/2 and 1/2–3/2 quantum mixtures including it, are much less well known. These have only rarely been invoked in recent years as an explanation for experimental haem protein magnetic data.
Can free energy transduction be localized at some crucial part of the enzymatic cycle?
Authors: Hill Terrell L. , Eisenberg Evan
Published: March 2009

Our concern here will be with energetic rather than kinetic aspects of how a macromolecular enzyme molecule or enzyme complex in a biological membrane accomplishes the transfer or transduction of one kind of small-molecule free energy into another. An example is the use of the free energy of ATP hydrolysis (to form ADP and P1) to move Ca2+ across a membrane against its own electrochemical potential gradient (Stryer, 1981). In this case, the free energy decreases in the hydrolysis reaction but much of this is recovered in the form of an increase in free energy of the Ca2+ ions (the remainder is dissipated as heat). There is, of course, no net change in the free energy of the enzyme itself (Ca-ATPase).
Relaxation studies of ion transport systems in lipid bilayer membranes
Authors: Läuger P. , Benz R. , Stark G. , Bamberg E. , Jordan P. C. , Fahr A. , Brock W.
Published: March 2009

Relaxation techniques have been widely used in kinetic studies of chemical reactions in homogeneous solution (Eigen & DeMayer, 1963). The principle of this method is well known: an external variable such as temperature or pressure is suddenly changed and the time course of a state parameter of the system such as concentration is recorded as it approaches a new steady value. Relaxation techniques can also be used for studying the rate of elementary processes in membranes. This method has proved particularly useful for the investigation of ion transport systems (ion carriers, channels, pumps) in artificial planar bilayer membranes. In this review we describe different relaxation techniques which have been developed for this purpose during the last years, as well as applications to a number of ion transport systems.
Visual control of orientation behaviour in the fly: Part I. A quantitative analysis
Authors: Reichardt Werner , Poggio Tomaso
Published: March 2009

An understanding of sensory information processing in the nervous system will probably require investigations with a variety of ‘model’ systems at different levels of complexity.

Our choice of a suitable model system was constrained by two conflicting requirements: on one hand the information processing properties of the system should be rather complex, on the other hand the system should be amenable to a quantitative analysis. In this sense the fly represents a compromise.

In these two papers we explore how optical information is processed by the fly's visual system. Our objective is to unravel the logical organization of the fly's visual system and its underlying functional and computational principles. Our approach is at a highly integrative level. There are different levels of analysing and ‘understanding’ complex systems, like a brain or a sophisticated computer.
Visual control of orientation behaviour in the fly: Part II. Towards the underlying neural interactions
Authors: Poggio Tomaso , Reichardt Werner
Published: March 2009

Visual information processing in the nervous system of flies begins with a large array of photoreceptors, which transduce a light intensity pattern, and culminates in a behavioural response that depends on that pattern.

In the previous paper we have given a quantitative description of visual control of flight orientation in the fly. This description can account for fixation, tracking and some instances of spontaneous pattern preference behaviour. The phenomenological theory outlines the basic logical organization of the visual control system of the fly. It requires the neural network between the receptors and the flight muscles to perform two main computations on the visual input. One computation extractsmovementinformation (the termr(ψ)ψ b of the phenomenological equation). The other provides position information (the termD(ψ)).
Conformational theory applied to polysaccharide structure
Authors: Brant David A.
Published: March 2009

Theoretical methods of conformational analysis have been applied to the biopolymers with beneficial consequences for the elucidation of structure–function relationships in these molecules. The methodology of theoretical conformational analysis and the fruits of its application to the biopolymers, particularly the polypeptides, have been the subject of numerous reviews (Ramachandran & Sasisekharan, 1968; Scheraga, 1968; Venkatachalam & Ramachandran, 1969; Scheraga, 1971; Brant, 1972; Hopflnger, 1973). A critical evaluation of these techniques as applied to the polynucleotides has recently appeared (Olson, 1975 a, b).
Determination of motile behaviour of prokaryotic and eukaryotic cells by quasi-elastic light scattering
Authors: Chen Sow-Hsin , Hallett Frederick Ross
Published: March 2009

Information on the swimming motion of microscopic calls and the factors which affect it is important to a wide range of disciplines. The functions of the motile apparatus of simpler organisms such as bacteria or algae can provide useful clues on the operation of more complex contractile systems such as muscles. Often celluar motility is a response to conditions external to the cell (e.g. chemotaxis) and, hence, can lead to increased understanding of the cell's sensory capability. On the medical front there is a physical similarity between the flagellar beat of the motile spermatozoa and the ciliary activity of epithelial lining of respiratory and reproductive tracts. Impairment of the motile apparatus can lead to sterility and to a variety of pathological conditions. In animal husbandry, in the artificial insemination industry and in sperm banking estimates of the extent of cellular motility and the fraction of cells which are motile are key quantities which can determmine the fertilization capability of a semen sample.
Lanthanides as probes for calcium in biological systems
Authors: Martin Bruce , Richardson Frederick S.
Published: March 2009

Calcium ion plays an essential role in many biological processes. The environment about Ca2+may be probed by substitution of tripositive lanthanide ions, Ln3+. Ca2+proteins fall into two broad classes: those that are inhibited by Ln3+substitution and those that are not. It is suggested that although Ca2+undertakes a primarily structural role in the Ln3+non-inhibited proteins, Ca2+may be near the active site or participate in the mechanism of action of Ln3+inhibited proteins. Ca2+and Ln3+radii are similar; most Ln3+are slightly larger than Ca2+in complexes of the same coordination number, and substitution of Ln3+for Ca2+is accommodated by a slight decrease in bond distance or by an increase in coordination number. Luminescence from Tb3+has been demonstrated to be a sensitive environmental probe of Ca2+binding sites in proteins.
Applications of Pulse Radiolysis to Protein Chemistry
Authors: Klapper M. H. , Faraggi M.
Published: March 2009

Since its introduction, pulse radiolysis has been an important technique for examining the properties of organic and inorganic radicals, and for enumerating those reactions responsible for cellular damage by ionizing radiation. Biochemists, and biophysicists outside the area of radiation biology appear, perhaps for historical reasons, to have an incomplete appreciation of the technique's potential. Protein chemists in particular, have been only dimly aware of the numerous reports of, and the significant results obtained from pulse radiolysis studies of proteins. Our purpose here is to bring some of these results together in order to emphasize the power and usefulness of pulse radiolysis experiments both for elucidating enzyme reaction mechanisms, and for gaining information on the structure of proteins in aqueous solutions. Reviews containing related, or in part the same material to be covered here have appeared previously; for example, Land (1970), Adamset al.(1972a), Shafferman & Stein (1975), Adams & Wardman (1977). This review updates these earlier works, but more importantly approaches the topic of protein pulse radiolysis with a different emphasis.
The study of enzyme mechanisms by a combination of cosolvent, low-temperature and high-pressure techniques
Authors: Douzou Pierre
Published: March 2009

It is generally assumed that the mechanism of enzyme-catalysed reactions would be defined if all the intermediates, complexes and conformational states of each enzyme could be characterized, and the rate-constants for their inter-conversion recorded. In spite of the introduction during the last decades of methods for rapid data acquisition, which permit detection of the number and sequence of intermediates and complexes, measurement of rate-constants, identification of the types of catalysis involved, etc., at best a semi-quantitative understanding of the mechanism of enzyme-catalysis is obtained. The definition of the exact chemical nature of intermediates and complexes is missing because techniques establishing the structures are restricted to the study of transient states which are stable for periods that exceed the half-life of most of typical intermediates. In such conditions, while conformational changes are obviously an essential feature of enzyme activity, the conformational basis of such activity cannot be understood at the molecular level, and enzyme catalysis is still termed a ‘miracle’ compared to the rate-enhancements and specificity of ordinary chemical catalysts.
Deuterium magnetic resonance: theory and application to lipid membranes
Authors: Seelig Joachim
Published: March 2009

Proton and carbon-13 nmr spectra of unsonicated lipid bilayers and biological membranes are generally dominated by strong proton–proton and proton–carbon dipolar interactions. As a result the spectra contain a large number of overlapping resonances and are rather difficult to analyse. Nevertheless, important information on the structure and dynamic behaviour of lipid systems has been provided by these techniques (Wennerström & Lindblom, 1977).
Fundamentals of drug design from a biophysical viewpoint
Authors: Van Gunsteren Wilfred F. , King Paul M. , Mark Alan E.
Published: March 2009

Drug design means many things to many people. Commercially the aim is the development of compounds that can be patented and meet a variety of regulatory standards. In drug design, for medical purposes, toxicity and bio-availability are major considerations.
Some recent applications of the use of paramagnetic centres to probe biological systems using nuclear magnetic resonance
Authors: Morris Arabella T. , Dwek Raymond A.
Published: March 2009

The explosion of the use of paramagnetic probes to study biological problems by nuclear magnetic resonance (n.m.r.) stems from the large and easily quantifiable perturbations they produce. The main reason for these perturbations is that the magnetic moments of unpaired electrons are about 103times greater than nuclear magnetic moments and consequently they generate much greater local fields.Such fields can give rise to large shifts in nuclear resonances; but if these fields fluctuate at the appropriate frequencies they will also cause very efficientrelaxationin the nuclear resonances. It is possible to select probes that result mainly in one of these parameters being perturbed so that the terms shift and relaxation probe are now well established in the literature.
Ca2+and activation mechanisms in skeletal muscle
Authors: Ashley Christopher C. , Mulligan Ian P. , Lea Trevor J.
Published: March 2009

It has been known for a number of years that calcium ions play a crucial role in excitation-contraction (e-c) coupling (Sandow, 1952). The majority of the calcium required for this process is derived, at least in vertebrate striated muscle fibres, from discrete intracellular stores located at sites within the cell: the terminal cysternae (tc)/junctional SR of the sarcoplasmic reticulum (SR) (Fig. 1 a). These storage sites not only form a compartment that is distinct from the sarcoplasm of the fibre, but they are also closely associated with the contractile elements, the myofibrils. The SR release sites are activated following the spread of electrical activity (Huxley and Taylor, 1958) along the transverse (T) tubular system (Eisenberg and Gage, 1967; Adrian et al. 1969a, b; Peachey, 1973) from the surface membrane (Bm).
Structure and function of tetanus and botulinum neurotoxins
Authors: Montecucco Cesare , Schiavo Giampietro
Published: March 2009

Tetanus and botulinum neurotoxins are produced byClostridiaand cause the neuroparalytic syndromes of tetanus and botulism. Tetanus neurotoxin acts mainly at the CNS synapse, while the seven botulinum neurotoxins act peripherally. Clostridial neurotoxins share a similar mechanism of cell intoxication: they block the release of neurotransmitters. They are composed of two disulfide-linked polypeptide chains. The larger subunit is responsible for neurospecific binding and cell penetration. Reduction releases the smaller chain in the neuronal cytosol, where it displays its zinc-endopeptidase activity specific for protein components of the neuroexocytosis apparatus. Tetanus neurotoxin and botulinum neurotoxins B, D, F and G recognize specifically VAMP/synaptobrevin. This integral protein of the synaptic vesicle membrane is cleaved at single peptide bonds, which differ for each neurotoxin. Botulinum A, and E neurotoxins recognize and cleave specifically SNAP-25, a protein of the presynaptic membrane, at two different sites within the carboxyl-terminus. Botulinum neurotoxin type C cleaves syntaxin, another protein of the nerve plasmalemma. These results indicate that VAMP, SNAP-25 a n d syntaxin play a central role in neuroexocytosis. These three proteins are conserved from yeast to humans and are essential in a variety of docking and fusion events in every cell. Tetanus and botulinum neurotoxins form a new group of zinc-endopeptidases with characteristic sequence, mode of zinc coordination, mechanism of activation and target recognition. They will be of great value in the unravelling of the mechanisms of exocytosis and endocytosis, as they are in the clinical treatment of dystonias.