Electron spin echo studies of cytochrome c oxidase

We have studied the linear electric field effect in pulsed EPR of the "EPR-detectable copper" signal of beef heart cytochrome c oxidase and have compared our results with those for a variety of square planar and tetrahedral Cu(II) model compounds and with Cu(II) proteins containing either type 1 or type 2 copper. The electric field induced g shifts (linear electric field effect) for cytochrome oxidase are comparable in magnitude to those for simple Cu(II) complexes and for some copper proteins containing type 2 sites. The shifts are smaller than those for tetrahedral copper complexes and for type 1 copper sites. However, the magnetic field dependence of the linear electric field effect does not resemble that observed for any Cu(II) complex studied nor for type 1 copper. These findings cannot be reconciled with the tetrahedral Cu(II) model proposed by Greenaway, Chan, and Vincow ((1977) Biochim. Biophys. Acta 490, 62-78, 1977) to explain the unusual EPR spectrum of cytochrome oxidase.     

Transient electric birefringence of colloidal particles immersed in shear flow. Part II. The initial response under the action of a rectangular electric pulse and the behavior at a low alternating electric field

The time-dependent rotational diffusion equation for rigid macromolecules in solution has been approximately solved for two cases in order to extend the electric birefringence technique to streaming-electric birefringence. One is for the initial period through the application of a rectangular electric pulse to the solution immersed in a low shear flow. The purpose of this is expansion of the distribution function into a function series made by the product of the powers of reduced time (= Thetat) and hydrodynamic field alpha (= G Theta , G: velocity gradient, Theta: rotary diffusion constant) and a surface harmonic P(i)(j)cos jphi. The solution for the build-up process at arbitrary electric field strength is found, but is limited to low hydrodynamic fields. The other is for the response when an alternating electric field is applied to the solution in a shear flow. Here, instead of reduced time, the maximum electric field E(0) is chosen as a parameter for the expansion. The expressions for the intensity of the transmitted light through crossed Nicols are derived in two optical systems where the polarizer is set at an angle of 45 degrees and 0 degrees to the direction of the electric field. The results in the former case show that we can determine four parameters, the ratio of velocity gradient to rotary diffusion constant, the axial ratio of a particle, the anisotropy of electric polarizability, and the optical anisotropy factor, from four values observed in two optical systems, namely, two light intensities before applying an electric field and two initial slopes of the build-up after applying an electric field. On the other hand, when a low alternating electric field with extremely high frequency is applied, the build-up of the light intensity in the former case is the same as that of electric birefringence for pure induced dipole orientation. The build-up for the latter optical system is the same as the expression for pure induced dipole orientation of Eq. (38) shown in a previous work.     

Effect of pulsed and reversing electric fields on the orientation of linear and supercoiled DNA molecules in agarose gels

When linear or supercoiled DNA molecules are imbedded in agarose gels and subjected to electric fields, they become oriented in the gel matrix and give rise to an electric birefringence signal. The sign of the birefringence is negative, indicating that the DNA molecules are oriented parallel to the electric field lines. If the DNA molecules are larger than about 1.5 kilobase pairs, a delay is observed before the birefringence signal appears. This time lag, which is roughly independent of DNA molecular weight, decreases with increasing electric field strength. The field-free decay of the birefringence is much slower for the DNA molecules imbedded in agarose gels than observed in free solution, indicating that orientation in the gel is accompanied by stretching. Both linear and supercoiled molecules become stretched, although the apparent change in conformation is much less pronounced for supercoiled molecules. When the electric field is rapidly reversed in polarity, very little change in the birefringence signal is observed for linear or supercoiled DNAs if the equilibrium orientation (i.e., birefringence) had been reached before field reversal. Apparently, completely stretched, oriented DNA molecules are able to reverse their direction of migration with little or no loss of orientation. If the steady-state birefringence had not been reached before the field reversal, complicated orientation patterns are observed after field reversal. Very large, partially stretched DNA molecules exhibit a rapid decrease in orientation at field reversal. The rate of decrease of the birefringence signal in the reversing field is faster than the field-free decay of the birefringence and is approximately equal to the rate of orientation in the field (after the lag period).(ABSTRACT TRUNCATED AT 250 WORDS)     

Numerical evaluation of currents induced in a worker by ELF non‐uniform electric fields in high voltage substations and comparison with experimental results

An ungrounded human, such as a substation worker, receives contact currents when touching a grounded object in electric fields. In this article, contact currents and internal electric fields induced in the human when exposed to non‐uniform electric fields at 50 Hz are numerically calculated. This is done using a realistic human model standing at a distance of 0.1–0.5 m from the grounded conductive object. We found that the relationship between the external electric field strength and the contact current obtained by calculation is in good agreement with previous measurements. Calculated results show that the contact currents largely depend on the distance, and that the induced electric fields in the tissues are proportional to the contact current regardless of the non‐uniformity of the external electric field. Therefore, it is concluded that the contact current, rather than the spatial average of the external electric field, is more suitable for evaluating electric field dosimetry of tissues. The maximum induced electric field appears in the spinal cord in the central nervous system tissues, with the induced electric field in the spinal cord approaching the basic restriction (100 mV/m) of the new 2010 International Commission on Non‐Ionizing Radiation Protection guidelines for occupational exposure, if the contact current is 0.5 mA. Bioelectromagnetics 34:61–73, 2013. © 2012 Wiley Periodicals, Inc.     

Investigation of electrorheological properties of biodegradable modified cellulose/corn oil suspensions

Considerable scientific and industrial interest is currently being focused on a class of materials known as electrorheological (ER) fluids, which display remarkable rheological behaviour, being able to convert rapidly and repeatedly from a liquid to solid when an electric field (E) is applied or removed. In this study, biodegradable cellulose was modified and converted to their carboxyl salts. Modified cellulose is characterised by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and conductivity measurements. Suspensions of cellulose (C) and modified cellulose (MC) were prepared in insulated corn oil (CO). The effects of electric field strength, shear rate, shear stress, temperature, etc. of these suspensions onto ER activity were determined. Rheological measurements were carried out via a rotational rheometer with a high-voltage generator to investigate the effects of electric field strength and particle concentration on ER performance.The results show that the ER properties are enhanced by increasing the particle concentration and electric field strength. Also the cellulose-based ER fluids exhibit viscoelastic behaviour under an applied electric field due to the chain formation induced by electric polarization between particles.     

Electric dipole theory and thermodynamics of actomyosin molecular motor in muscle contraction

Movements in muscles are generated by the myosins which interact with the actin filaments. In this paper we present an electric theory to describe how the chemical energy is first stored in electrostatic form in the myosin system and how it is then released and transformed into work. Due to the longitudinal polarized molecular structure with the negative phosphate group tail, the ATP molecule possesses a large electric dipole moment (p(0)), which makes it an ideal energy source for the electric dipole motor of the actomyosin system. The myosin head contains a large number of strongly restrained water molecules, which makes the ATP-driven electric dipole motor possible. The strongly restrained water molecules can store the chemical energy released by ATP binding and hydrolysis processes in the electric form due to their myosin structure fixed electric dipole moments (p(i)). The decrease in the electric energy is transformed into mechanical work by the rotational movement of the myosin head, which follows from the interaction of the dipoles p(i) with the potential field V(0) of ATP and with the potential field Psi of the actin. The electrical meaning of the hydrolysis reaction is to reduce the dipole moment p(0)-the remaining dipole moment of the adenosine diphosphate (ADP) is appropriately smaller to return the low negative value of the electric energy nearly back to its initial value, enabling the removal of ADP from the myosin head so that the cycling process can be repeated. We derive for the electric energy of the myosin system a general equation, which contains the potential field V(0) with the dipole moment p(0), the dipole moments p(i) and the potential field psi. Using the previously published experimental data for the electric dipole of ATP (p(0) congruent with 230 debye) and for the amount of strongly restrained water molecules (N congruent with 720) in the myosin subfragment (S1), we show that the Gibbs free energy changes of the ATP binding and hydrolysis reaction steps can be converted into the form of electric energy. The mechanical action between myosin and actin is investigated by the principle of virtual work. An electric torque always appears, i.e. a moment of electric forces between dipoles p(0) and p(i)(/M/ > or = 16 pN nm) that causes the myosin head to function like a scissors-shaped electric dipole motor. The theory as a whole is illustrated by several numerical examples and the results are compared with experimental results.     

Comparison of coupling of humans to electric and magnetic fields with frequencies between 100 Hz and 100 kHz

Recent laboratory and epidemiological results have stimulated interest in the hypothesis that human beings may exhibit biological responses to magnetic and/or electric field transients with frequencies in the range between 100 Hz and 100 kHz. Much can be learned about the response of a system to a transient stimulation by understanding its response to sinusoidal disturbances over the entire frequency range of interest. Thus, the main effort of this paper was to compare the strengths of the electric fields induced in homogeneous ellipsoidal models by uniform 100 Hz through 100 kHz electric and magnetic fields. Over this frequency range, external electric fields of about 25–2000 V/m (depending primarily on the orientation of the body relative to the field) are required to induce electric fields inside models of adults and children that are similar in strength to those induced by an external 1 μT magnetic field. Additional analysis indicates that electric fields induced by uniform external electric and magnetic fields and by the nonuniform electric and magnetic fields produced by idealized point sources will not differ by more than a factor of two until the sources are brought close to the body. Published data on electric and magnetic field transients in residential environments indicate that, for most field orientations, the magnetic component will induce stronger electric fields inside adults and children than the electric component. This conclusion is also true for the currents induced in humans by typical levels of 60 Hz electric and magnetic fields in U.S. residences. Bioelectromagnetics 18:67–76, 1997. © 1997 Wiley-Liss, Inc.     

Electric Imaging through Evolution,a Modeling Study of Commonalities and Differences

Modeling the electric field and images in electric fish contributes to a better understanding of the pre-receptor conditioning of electric images. Although the boundary element method has been very successful for calculating images and fields, complex electric organ discharges pose a challenge for active electroreception modeling. We have previously developed a direct method for calculating electric images which takes into account the structure and physiology of the electric organ as well as the geometry and resistivity of fish tissues. The present article reports a general application of our simulator for studying electric images in electric fish with heterogeneous, extended electric organs. We studied three species of Gymnotiformes, including both wave-type (Apteronotus albifrons) and pulse-type (Gymnotus obscurus and Gymnotus coropinae) fish, with electric organs of different complexity. The results are compared with the African (Gnathonemus petersii) and American (Gymnotus omarorum) electric fish studied previously. We address the following issues: 1) how to calculate equivalent source distributions based on experimental measurements, 2) how the complexity of the electric organ discharge determines the features of the electric field and 3) how the basal field determines the characteristics of electric images. Our findings allow us to generalize the hypothesis (previously posed for G. omarorum) in which the perioral region and the rest of the body play different sensory roles. While the “electrosensory fovea” appears suitable for exploring objects in detail, the rest of the body is likened to a “peripheral retina” for detecting the presence and movement of surrounding objects. We discuss the commonalities and differences between species. Compared to African species, American electric fish show a weaker field. This feature, derived from the complexity of distributed electric organs, may endow Gymnotiformes with the ability to emit site-specific signals to be detected in the short range by a conspecific and the possibility to evolve predator avoidance strategies.     

Effect of Blood Vessel Segmentation on the Outcome of Electroporation-Based Treatments of Liver Tumors

Electroporation-based treatments rely on increasing the permeability of the cell membrane by high voltage electric pulses applied to tissue via electrodes. To ensure that the whole tumor is covered with sufficiently high electric field, accurate numerical models are built based on individual patient anatomy. Extraction of patient''s anatomy through segmentation of medical images inevitably produces some errors. In order to ensure the robustness of treatment planning, it is necessary to evaluate the potential effect of such errors on the electric field distribution. In this work we focus on determining the effect of errors in automatic segmentation of hepatic vessels on the electric field distribution in electroporation-based treatments in the liver. First, a numerical analysis was performed on a simple ''sphere and cylinder'' model for tumors and vessels of different sizes and relative positions. Second, an analysis of two models extracted from medical images of real patients in which we introduced variations of an error of the automatic vessel segmentation method was performed. The results obtained from a simple model indicate that ignoring the vessels when calculating the electric field distribution can cause insufficient coverage of the tumor with electric fields. Results of this study indicate that this effect happens for small (10 mm) and medium-sized (30 mm) tumors, especially in the absence of a central electrode inserted in the tumor. The results obtained from the real-case models also show higher negative impact of automatic vessel segmentation errors on the electric field distribution when the central electrode is absent. However, the average error of the automatic vessel segmentation did not have an impact on the electric field distribution if the central electrode was present. This suggests the algorithm is robust enough to be used in creating a model for treatment parameter optimization, but with a central electrode.     

Analysis of the differential cross sections for bremsstrahlung during collisions between two charged particles in a uniform electric field

Under the nonrelativistic Born approximation, differential cross sections are derived for elastic collisions between two point charged particles in an external constant uniform electric field and for bremsstrahlung during these collisions.An analysis of the cross sections obtained shows that, due to the interference of the wave functions of two colliding particles during their reflection from the potential barrier of an external electric field, the differential cross sections for elastic collisions and for unpolarized bremsstrahlung (i) are both oscillatory in character and (ii), instead of being linearly proportional to one another (as in the case without an externale electric field), are related in a more complicated manner.     

Modification of electrokinetic properties of nuclei in human buccal epithelial cells by electric fields

The influence of an alternating (50 Hz) electric field (5--110 V/cm) on the state of human buccal epithelium cells was studied by the methods of intracellular microelectrophoresis, heterochromatin staining with orcein, and indigo carmine staining for viability and membrane integrity evaluations. Electric field exposure induced an increase in electrophoretic mobility of cell nuclei, decreased numbers of heterochromatin granules near the inner membrane of cell nucleus, and induced cell membrane damage; but cell viability was conserved. Nuclear and cell membrane properties varied with electric field strength and age of the donors. The data obtained are interpreted as evidence of electric field induced activation of the functional state of nuclei.     

Perturbation of a collisional plasma by exterior bodies in a uniform external electric field

The charging of a metal sphere in a weakly ionized collisional plasma in a uniform external electric field is investigated with allowance for the effect of the space charge field and ionization-recombination processes. The sphere charge and the spatial distributions of charged plasma particles are calculated both numerically and analytically (for some particular cases) for the case of a strong external field. It is found that the size of the perturbed plasma region is determined by the external field and the intensity of recombination processes. It is shown that the total electric charge (the sphere charge plus the plasma space charge) is zero in accordance with predictions of the theory of static currents in a conducting medium.     

Kinetic Theory Model for Ion Movement through Biological Membranes: I. Field-Dependent Conductances in the Presence of Solution Symmetry

A model for ion movement through specialized sites in the plasma membrane is presented and analyzed using techniques from nonequilibrium kinetic theory. It is assumed that ions traversing these specialized regions interact with membrane molecules through central conservative forces. The membrane molecules are approximated as massive spherical scattering centers so that ionic fractional energy losses per collision are much less than one. Equations for steady-state membrane ionic currents and conductances as functions of externally applied electric field strength are derived and numerically analyzed, under the restriction of identical solutions on each size of the membrane and constant electric fields within the membrane. The analysis is carried through for a number of idealized ion-membrane molecule central force interactions. For any interaction leading to a velocity-dependent ion-membrane molecule collision frequency, the membrane chord conductance is a function of the externally applied electric field. Interactions leading to a collision frequency that is an increasing (decreasing) function of ionic velocity are characterized by chord conductances that are decreasing (increasing) functions of field strength. For ion-neutral molecule interactions, the conductance is such a rapidly decreasing function of field strength that the slope conductance becomes negative for all field strengths above a certain value.     

Limited trypsinolysis changes in structural dynamics of myosin subfragment 1

The effects of limited trypsinolysis of myosin subfragment 1 (S1) on its structural dynamics were investigated by using the method of transient electric birefringence. Conversion of S1 by trypsin to produce S1 (T) did not change the specific Kerr constant [(8.1 +/- 0.3) X 10(-7) and (8.0 +/- 0.3) X 10(-7) cm2/statvolt2 for S1(T) and S1, respectively] or the degree of alignment in a weak electric field, suggesting that the size of S1 and its permanent electric dipole moment are not modified by trypsin. On the other hand, the relaxation time for the field-free rotation, after achieving a steady-state birefringence signal, was reduced from 316 ns for S1 to 269 ns for S1(T), at 3.7 degrees C, suggesting that trypsinolysis increases the flexibility of the connections between S1 segments or introduces additional segmental motions. For both S1 and S1(T), the rate of decay for a steady-state signal was independent of the field strength, between 3.34 and 20.3 statvolt/cm. Shortening the duration of the weak electric field pulses to 0.35 microseconds, so that steady-state signals were not achieved, decreased the relaxation times for S1 and S1(T) to 240 and 210 ns, respectively, which is consistent with the segmented flexible S1 structure proposed earlier [Highsmith, S., & Eden, D. (1986) Biochemistry 25, 2237]. When the strength of the electric field was increased to above 10 statvolt/cm, in order to make the interaction energy for the S1(T) electric dipole moment in the electric field greater than the thermal energy, the relaxation time after a 0.35-microseconds pulse decreased from 210 to 170 ns as the field was increased from 7 to 20 statvolt/cm. (ABSTRACT TRUNCATED AT 250 WORDS)     

The electrophoretic hemolytic plaque assay - theory

We use the mathematical theory of plaque growth to determine if there is merit in performing a hemolytic plaque assay in the presence of an external electric field. In particular, we study the effects of an electric field on the transport of anti-bodies secreted by a single lymphocyte and on the size and shape of the plaques they produce. Our results indicate that in the presence of an applied electric field: (1) The mobility of the antibodies produced by the antibody forming cell can be determined from the plaque shape. (In the electric field the plaques are no longer circular, but cigar shaped.) (2) By changing the magnitude or direction of the applied electric field more than one plaque can be generated by a single AFC. Thus changes in mobility or the rate of antibody secretion can be assayed. (3) Plaques will reach a steady state size; for good emitters (cells that secrete antibodies at a high rate or that secrete high affinity antibodies) this steady state will be achieved rapidly.Equations are given which describe both the temporal development and steady state plaque size and shape. From the equations, computer generated plots of plaques produced by typical antibody farming cells are presented. These plots are then used to show how pictures of plaques formed in an electric field can be analyzed to determine the antibody mobility.     

Electrooptic study of the deionized form of bacteriorhodopsin

Electric field induced light scattering by suspensions of cation-depleted purple membranes, obtained by deionization of purple membrane (PM) suspensions on a cation exchange column or by electrodialysis at a pH around 6, shows a strong drop (more than 5 times) in the value of the permanent dipole moment relative to that of PM fragments. The membrane dipole moments were measured both at low dc and ac electric fields as well as by using electric field pulses with reversing polarity. Some slight changes in the dispersion of the electric polarizability were also observed.Microelectrophoretic measurements showed that the electric charge of the membrane fragments is increased by 30% after deionization. The importance of these data for the understanding of the blue membrane properties and subsequently for the mechanism of proton pumping are discussed.     

A Computational Study of the Giant Local Electric Field Enhancement in Al-Au-Ag Trimetallic Three-Layered Nanoshells

The surface plasmon resonance (SPR)-induced local field effect in Al-Au-Ag trimetallic three-layered nanoshells has been studied theoretically. Because of having three kinds of metal, three plasmonic bands have been observed in the absorption spectra and the local electric field factor spectra. The local electric field enhancement and the corresponding resonance wavelength for different plasmon coupling modes and spatial positions of the Al-Au-Ag nanoshells with various geometry dimensions are investigated to find the maximum local electric field enhancement. The calculation results indicate that the giant local electric field enhancement could be stimulated by the plasmon coupling in the middle Au shell or the outer Ag shell and could be optimized by increasing the Ag shell thickness and decreasing the Au shell thickness. What is more, the local electric field enhancement also nonmonotonously depends on the dielectric constant of the environment; the local electric field intensity will be weakened when the surrounding dielectric constant is too small or too large.

     

Observation of DNA molecules undergoing capillary electrophoresis.

This paper presents a method to observe the motions and configurations of large DNA molecules undergoing capillary electrophoresis (CE). A simple device to perform CE horizontally under microscopic observation is designed and images of single DNA molecules inside the capillary are obtained using an epi-fluorescence microscope. DNA molecules moved towards the negative electrode when an electric field was applied. The mobilities of three types of DNA (T4 and lambda bacteriophage DNA and PBR322 plasmid DNA) were measured at different electric field strength. The mobility vs. electric field strength curves of these three large DNAs showed that the mobility remained constant at high electric field strength (200-600 Volt/cm) and increased significantly at low electric field strength (less than or equal to 50 Volt/cm.). The apparent mobilities of the large DNA molecules were independent of molecular weight. At electric field strengths greater than or equal to 400 Volt/cm., big aggregates (snowballs) of DNA molecules formed and moved upstream towards the positive electrode. When the field was turned off, the aggregates dissociated into a cloud of single DNA molecules, and diffused into the solution.     

The embryonic development of Xenopus laevis under a low frequency electric field

The aim of this study was to determine the effects of a low frequency electric field on the early embryonic development of frogs. The embryos of African clawed toads, Xenopus laevis, were exposed to a 20-μA electric current during the cleavage stages. The developmental processes of embryos during and after electric field exposure were monitored for teratogenic effects. All the embryos continuously exposed to the electric field died without undergoing any developmental processes. However, when the embryos were exposed to the electric field for 20-min periods (four times/over 2 d), the embryos developed into both normal tadpoles (70 %) and malformed tadpoles with light edema, reduced pigmentation, or axial anomalies, such as crooked tails. After exposure, the control embryos were at development stage 35.5 (2 d 2 h), while the normal embryos of the assay group were at developmental stage 41(3 d 4 h). There was a 1 d 2 h difference between the two developmental stages, revealing the importance of that time period for embryogenesis. In conclusion, the effects of electric current on Xenopus embryos are dependent on the initial developmental stage and the duration of exposure.