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At least 811 records · Page 45Linked to original sources
PubMed1978

The influence of electrostatic and magnetic fields on mutation in Drosophila melanogaster spermatozoa.

Canton-S Drosophila melanogaster males were exposed to electrostatic and magnetic fields for 24 h to determine the influence of low energy fields on the production of sex-linked recessive lethal mutations in the mature, motile sperm. To detect sex-linked recessive lethal production in mature sperm the standard Muller-5 test was done. Exposure of the males to the magnetic field or the electrostatic field did not significantly affect the mutation frequency in mature sperm.

Animals↗
PubMed1985

Electrostatics and flexibility in protein-DNA interactions.

CAP, cro, and lambda repressor represent a class of gene-regulatory proteins that bind specifically to DNA using a common bihelical motif. Examination of these structures suggest a possible mechanism for the binding of protein to DNA. The first step would be the formation of a non-specific protein-DNA complex energetically driven by the electrostatic interaction of asymetrically distributed charges on the surface of the protein that complement the charges on DNA. This attraction keeps the protein near the DNA, limiting diffusion to one dimension. As the protein slides, random thermal fluctuations twist and dip the protein over irregularities in the structure of the DNA. During these excursions, surface complementarity is sampled until the specific binding site is found. At this point the intervening solvent is displaced allowing the two molecules maximize their electrostatic and hydrogen bonding interactions.

Amino Acid Sequence↗
PubMed1996

Electrostatic parameters of the theoretical quaternary structure of bovine alpha-crystallin.

By changing the ionic strength, the effects of charge modification on the electrostatic properties of our predicted "open' micellar quaternary structure composed of bovine alpha A subunits were determined. The electrostatic potential values (phi) at 6 arbitrary points surrounding the protein and at all atomic sites of the protein were calculated using the non-linear Poisson-Boltzmann equation. The effective charge (q) of our predicted aggregate ranged from 16 at 0.0022 M to 45 at 0.1472 M ionic strengths. The variation of potential (phi), as well as charge, is a hyperbolic function of ionic strength (R2, 0.901). Plotting the inverse charge (l/q) against inverse ionic strength (1/l) it is possible to calculate maximum charge (q(max)) (approximately 48) at saturation. This value is close to previously reported experimental (50 +/- 5), and our theoretical charge (45), values at physiological ionic strength (0.145 M). These data indicate that maximal repulsion among the alpha-crystallin aggregates occurs at or near physiological ionic strength. Also, half-maximal charge (q(max)/2) at 0.003-0.004 M indicates a transition state at very low ionic strength. The calculated volume available for the mobile solvent in our quaternary structure is approximately 70%. These data are in good agreement with experimental values for bovine alpha-crystallin in solution reported by Xia et al. (Biophys. J., 1994; 66: 861-872). This agreement provides support for our predicted models of alpha-crystallin and a level of confidence in the reliability of the theoretical calculations. Since an ionic gradient exists between the lens cortical and nuclear regions, the modification of charge on alpha-crystallin by varying ionic strength could contribute to the function of alpha-crystallin as a modulator of lens supermolecular order during fiber cell maturation.

Animals↗
PubMed1992

Effect of electrostatic forces on the dynamic rheological properties of injectable collagen biomaterials.

Injectable collagen is a concentrated dispersion of phase-separated collagen fibres in aqueous solution used to correct dermal contour defects through intradermal injection. The effect of electrostatic forces on the rheology of injectable collagen was studied by observation of the birefringence of collagen fibres through a polarizing microscope as well as by oscillatory rheological measurements on dispersions of varying ionic strengths (0.06-0.30). The birefringence of fibres progressively increased as ionic strength was reduced from 0.30 to 0.06. The linear viscoelastic measurements displayed a logarithmic relationship between storage (and loss) moduli and frequency over oscillation frequencies of 0.1-100 rad/s. The associated relaxation time spectra, interpreted using the theory of Kamphuis et al. for concentrated dispersions, show that collagen fibres become more flexible as ionic strength increases. This result was analysed at the molecular level from the perspective that collagen fibres are a liquid-crystalline phase of rigid rod collagen molecules which have phase-separated from solution. Electrostatic forces affect the volume fraction of water present in the collagen fibres which in turn alters the rigidity of the fibres. Flexible collagen fibre dispersions displayed emulsion-like flow properties whereas more rigid collagen fibre dispersions displayed suspension-like flow properties. Changes in fibre rigidity significantly alter the injectability of collagen dispersions which is critical in clinical performance.

Animals↗
PubMed1995

Adhesion of leucocytes to microscope slides as influenced by electrostatic interaction.

The adhesion of leucocytes to standard microscope slides is low, which severely limits the cell recovery in cytological preparations on such slides. We coated the slides with various polycations with the aim of achieving an electrostatic surface charge which would increase the cell adhesion but would still avoid cell disruption. The adhesion of leucocytes from a K562 myeloid cell suspension and from cerebrospinal fluid was measured on standard slides made of glass and of oxidized polystyrene, and on slides coated with several chemically different cationic polymers. The electrostatic surface charge and the surface tension of these matrices were determined. We found the cell adhesion to be significantly higher on the matrices with a more attractive zeta potential and not to be measurably influenced by the surface tension of the matrices. The results help to improve the cytological preparation technique, especially for suspensions with a low cell content.

Analysis of Variance↗
PubMed1983

Use of local electrostatic environments of cysteines to enhance formation of a desired species in a reversible disulfide exchange reaction.

The role of electrostatic factors has been evaluated for the reversible disulfide exchange reaction between N-acetylcysteine (A) and a peptide fragment (B) comprising residues 85-114 of Kunitz soybean trypsin inhibitor. In A, the sulfhydryl group has a negative carboxyl neighbor on the cysteine itself. In B, the only charged group within five residues of the single cysteine at position 86 is the positive N-terminal amino group on residue 85. The concentrations of the monomers A and B and of the disulfides AA, AB and BB have been determined as a function of time in kinetic experiments at pH 7, 23 degrees C and ionic strengths of 20 mM and 1 M. At both ionic strengths the sulfhydryl acid dissociation constants Ka have been determined for A and B, as well as the four rate constants for the disulfide exchange reaction. The electrostatic effects are small in magnitude but occur in expected directions. Local cysteine environments enhance formation of the mixed disulfide (AB), having a favorable configuration of adjacent unlike charges and generate decreases in the AA and BB disulfides joining regions of identical charge. These experiments represent an initial step towards use of intrinsic protein functional groups to direct formation of specific disulfides in a synthetic protein.

Acetylcysteine↗
PubMed1988

Allowance for effects of electrostatic repulsion on protein dimerization.

A simple procedure for assessing the extent of electrostatic effects on protein dimerization is described and illustrated by application to published results on the ionic strength dependence of the dimerization constant for alpha-chymotrypsin at pH 4 (Aune, K.C., Goldsmith, L.C. and Timasheff, S.N. (1971) Biochemistry 10, 1617-1622). From the analysis it is concluded that the inverse dependence of alpha-chymotrypsin dimerization upon ionic strength is predominantly a general electrostatic effect, rather than a consequence of repulsion between two specific charged residues on the adjacent monomers comprising dimer.

Chemical Phenomena↗
PubMed1991

Electrostatic effects in the alpha-chymotrypsin-catalyzed acyl transfer. I. Influence of different inorganic salts.

We investigated the deacylation of two acyl-alpha-chymotrypsins by added nucleophiles. The nucleophile binding site of the enzyme shows a strong preference for positively charged compounds. Most of our data can be explained by direct electrostatic interaction between the ionic nucleophiles and two negatively charged residues which are located close to the active site of the enzyme molecule. The influence of inorganic salts on the acyl transfer includes the following effects: (1) reduction of electrostatic interactions between the acyl-enzyme and the nucleophile by addition of salts; (2) binding of divalent cations to the nucleophile binding site of the acyl-enzyme leading to a significantly changed specificity; and (3) linear dependence of the activity coefficients of the added nucleophiles on salt concentration.

Acylation↗
PubMed1989

A graphical representation of the electrostatic potential and electric field on a molecular surface.

The graphics program presented, ARCHEM, draws the molecular electrostatic potential (MEP) on a molecular surface color-coded according to the magnitude of the potential. Vectors can be drawn on the surface to show the electric field surrounding the molecule and color-coded according to the magnitude of the field. The electrostatic potential (ESP) calculated from the wave function or from net atomic charges using GAUSSIAN 80 UCSF1.2 can be plotted at points on a shell surrounding the molecule. For the neurotransmitter glycine zwitterion, the MEP is calculated from the wave function and from different point charge models, and the results are represented graphically.

Computer Graphics↗
PubMed1990

The use of the electrostatic potential at the molecular surface in recognition interactions: dibenzo-p-dioxins and related systems.

An ab initio self-consistent-field molecular orbital approach was used to compute the electrostatic potentials of dibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), two analogues of the latter, and two isomeric benzoflavones on a three-dimensional molecular surface corresponding to the contour of constant electronic density equal to 0.002 electrons/bohr3. The results are discussed in relation to the biological activities of the respective molecules. It is shown that the electrostatic potential graphically depicted on the molecular surface is well suited for the study of recognition interactions, such as are believed to be involved in the initial receptor-mediated step leading to toxicity in the dibenzo-p-dioxins. The surface potential has the advantage of clearly showing steric features that may play a role in understanding the recognition process being investigated.

Computer Graphics↗
PubMed1991

Calculation and display of electrostatic potentials.

A general methodology is developed for incorporating accurate electrostatic information from ab initio molecular orbital calculations into molecular mechanics calculations. Examples are given of the method applied to simple aromatic organic molecules. A program has been developed for displaying the results of the ab initio calculations on a Silicon Graphics workstation. The technique developed here provides an alternative method for including electrostatic interactions in molecular mechanics calculations and is compared with other methods for determining atomic charges.

Computer Graphics↗
PubMed1991

Efficient method for the generation and display of electrostatic potential surfaces from ab-initio wavefunctions.

A cost effective color graphics representation of molecular electrostatic potential surfaces employing the cumulative atomic or bond multipole moments has been described. A general description of the method used to obtain cumulative multipole moments directly from ab-initio wavefunctions is given, along with an outline of the algorithm for generating electrostatic potential surfaces in the molecular graphics programs MOL17 (FORTRAN 77, Silicon Graphics 3130 and 4D series workstations) and PCMCAMM (Turbo Pascal, IBM PC and PS/2 computers). Examples are given that illustrate the convergence of the multiple expansion, the degree of basis-set dependence compensated by the use of higher atomic moments, and the effect of placing additional expansion centers along the bonds.

Amino Acids↗
PubMed1995

Substrate recognition by ribosome-inactivating protein studied by molecular modeling and molecular electrostatic potentials.

A computer model of dianthin 30, a type 1 ribosome-inactivating protein (RIP), is constructed by homology modeling using two known X-ray structures; a type 1 RIP, pokeweed antiviral protein (PAP), and chain A of a type 2 RIP, ricin. The 3D structure is refined by molecular dynamics and its binding site compared with those of PAP and ricin using molecular electrostatic potential mapping. The differences in the maps obtained clearly show how, despite the similarity of the topology of the binding site, differences in electrostatic potential can account for the experimentally observed differences in substrate recognition and binding. This demonstrates the potential of these techniques for guiding further experimental analyses.

Amino Acid Sequence↗
PubMed1995

Interrelation between electrostatic and lipophilicity potentials on molecular surfaces.

Molecular electrostatics and lipophilicity are two important properties included in quantitative structure-activity relationships (QSARs) employed for rational drug design. The molecular electrostatic potential (MEP) provides information on the position, distribution, and extent of electrophilic and nucleophilic regions around a molecule. Similarly, the solvent affinity can be represented by a local phenomenological potential of semiempirical nature: the molecular lipophilicity potential (MLP). Although a simultaneous, three-dimensional display of MEP and MLP is possible, it may not provide a practical tool for comparing molecules. In this work, we deal with the simpler two-dimensional maps of the entire molecular surface projected onto an MEP-MLP plane. We analyze how these maps change with the following factors: (1) composition and molecular geometry, (2) the quality of the computation of MEP, and (3) the parameter set used for evaluating the lipophilicity potential. The approach is used to compare series of pyrazole derivatives. The methodology is useful in assessing molecular similarity, as well as in establishing the nature of differences between compounds.

Chemical Phenomena↗
PubMed1995

Contribution of electrostatic and hydrophobic interactions to the adsorption of proteins by aluminium-containing adjuvants.

The effect of ionic strength and ethylene glycol on the adsorption of bovine serum albumin (BSA) or lysozyme by a commercial aluminium hydroxide or aluminium phosphate adjuvant was studied at pH 7.4 and 25 degrees C. The adsorption of BSA by aluminium hydroxide adjuvant and lysozyme by aluminium phosphate adjuvant was found to be inversely related to ionic strength. This indicates that electrostatic attractive forces contribute to adsorption. The adsorption of lysozyme by aluminium phosphate adjuvant was reduced by the addition of ethylene glycol. However, no change in the adsorption of BSA by aluminium hydroxide adjuvant was noted when up to 40% ethylene glycol was present. This behaviour indicates that hydrophobic forces contribute to the adsorption of lysozyme but not of BSA. However, virtually no adsorption was observed when the protein and the adjuvant had the same surface charge. Thus, attractive forces may not be sufficient to produce adsorption of an antigen by an aluminium-containing adjuvant if electrostatic repulsive forces are present.

Adjuvants, Immunologic↗
PubMed1994

Involvement of electrostatic interactions in cytochrome c complex formations.

Structural studies on various electron transfer complexes involving the tetrahemic cytochrome c3 provided evidence that one of the hemes (heme 4) is the interacting site on the molecule. The reactivity of this particular heme is allocated to the positive charges found around the heme group which are strongly involved in the electrostatic interaction processes. Electrostatic and hydrophobic effects in complex formation are considered on the basis of two electron transfer complex examples: the soluble cytochrome c-cytochrome c peroxidase and the membrane bound photosynthetic reaction center.

Amino Acid Sequence↗
PubMed1976

Electrostatic free energy and shift of the phase transition for charged lipid membranes.

For a charged membrane in an electrolyte solution the electrostatic free energy is derived treating the system as a diffuse double layer. The dependence of the energy on external parameters like surface charge density and temperature is obtained and the physical basis discussed. As an application the charges are shown to exert an electrostatic surface pressure on the lipid chain packing which leads to a shift in the phase transition of membranes. The results confirm the interpretation of experimental data as given by Träuble et al. in the accompanying paper.

Lipids↗
PubMed1981

Energy barriers for passage of ions through channels. Exact solution of two electrostatic problems.

Exact solutions are given to two electrostatic problems relevant to ion permeation through pores in membranes. The first assesses the importance of the pore forming molecule as a dielectric shield. It is shown on the basis of structural and dielectric considerations alone (neglecting effects attributable to possible charge distribution at the interior surface of the pre-former) that the minimum electrostatic barrier for monovalent ion passage through a gramicidin-like channel is 11 kT. It is further shown that given favorable circumstances, dielectric shielding might dramatically reduce the barrier to ion passage through potassium channels. The second problem considers the error introduced by treating ions as point charges. It is shown that for structureless pores the point charge approximation introduces no meaningful error, even if the ratio of ion radius to pore radius is as great as 0.95.

Gramicidin↗