Dielectric behavior of DNA solution at radio and microwave frequencies (at 20 degrees C).

The dielectric constant and conductivity of calf thymus DNA were investigated at frequencies between 0.1 MHz and 70 GHz. This work is to investigate the dielectric properties of DNA in low gigahertz region and also to study whether the dielectric behavior of the water is affected by the presence of highly charged DNA. The results of these measurements indicate the presence of two anomalous dispersions, the one between 1 MHz and 1 GHz and the second one above 1 GHZ. The dispersion at low frequencies is likely to arise from polar groups in the DNA molecule. The relaxation behavior of unbound water in DNA solution is only slightly affected by the presence of DNA at concentrations below 1%.     

Morphological appearance of epidermal cells cultured on fibroblast-reorganized collagen gels

Summary Human foreskin fibroblasts were used to reorganize hydrated collagen gels into a dermal-like matrix, after which freshly isolated keratinocytes isolated from rabbit ear skin were placed on the surfaces of the matrices and cultured for up to 12 days. Transmission electron microscopy revealed 8–12 cell layers of epidermal cells organized in three distinct strata. The basal stratum consisted of cuboidal to columnar cells with typical complement of organelles, oval nuclei, and prominent tonofilaments inserting into desmosomes. Mitotic cells often were found at this level. There was no well-defined basement membrane region; rather, many of the cells appeared to be in close contact with collagen fibrils. The intermediate stratum of suprabasal cells consisted of elongated cells that had reduced organelles, but still were connected to each other by desmosomes. Finally, the superficial stratum of suprabasal cells contained cells that were completely flattened and often appeared to be sloughing off the apical surfaces of the cultures. Indirect immunofluorescence studies carried out on frozen sections revealed bullous pemphigoid antigen associated with basal epidermal cells; pemphigus vulgaris antigen around the epidermal cells of all strata, and keratin present in the epidermal cells of all strata. Filaggrin was observed in punctate and fibrillar arrangements in suprabasal cells. Fibronectin was found in a linear deposit at the dermal-epidermal junction and around the fibroblasts in the reorganized collagen gels. Type-IV collagen and laminin, however, were not detected.     

Dielectric constant of sickle cell hemoglobin. Dielectric properties of sickle cell hemoglobin in solution and gel

The dielectric constants of sickle cell hemoglobin were determined before and after gelation. The dielectric properties of oxy and deoxy sickle cell hemoglobin in solution are nearly identical to those of oxy and deoxy hemoglobin A. Only in the gel state did deoxy sickle cell hemoglobin display dielectric behavior different from that in solution. Upon gelation of deoxy sickle cell hemoglobin, the dielectric constant showed a marked decrease, and the relaxation frequency shifted towards higher frequencies. This result suggests that dielectric constant measurement can be used for the investigation of the kinetics of polymerization of sickle cell hemoglobin molecules. Despite the marked decrease in the dielectric constant, deoxy sickle cell hemoglobin still showed a well-defined dielectric dispersion even in the gel state. This indicates that individual molecules have considerable freedom of rotation in gels. It was observed that the dielectric properties of gelled deoxy sickle cell hemoglobin were affected by electrical fields at the level of 10 to 20 V/cm. This observation suggests that electrical fields of moderate strengths are able to perturb the gel structure if the system is near the transition region. The non-linear electrical behavior of gelled sickle cell hemoglobin will be discussed further in subsequent papers.     

Study of dielectric behavior of DNA in shear gradient

The dielectric behavior of the DNA molecule is investigated in the presence of mechanical force as well as the electrical field. In the present experiment, the direction of the electrical field is perpendicular to that of the mechanical force. The dipole moment of polar molecules manifest itself as dielectric increment at low frequencies or as the conductance increment at high frequencies. These two quantities are closely related to each other by Eq. (1) in the text. Because of the difficulty due to electrode polarization at low frequencies, no useful information was obtained by investigating the dielectric increment in the present system. Therefore, the effect of shear gradient was studied by measuring the conductance increment at high frequencies with various velocity gradients. The conductance increment decreased when the shear was applied perpendicular to the electrical field. The conductance change is converted into the unit of dielectric constant; it was found that the dielectric increment of DNA solution decreases by as much as 85 percent. From these observations, it is concluded that the direction of the dipole moment in DNA is longitudinal rather than transverse. The same experiment was repeated with the random coil DNA and no anisotropy in the dielectric increment was observed.     

Optical anisotropy of synthetic polynucleotides. II. Calculation of pi-electron polarizability of uracil and adenine

The interchain packing energy of two-, three-, and four-stranded α-helical ropes has been investigated. Poly-L -alanine was chosen as a model, and the interchain energies were calculated for various combinations of chain sense as a function of interchain distance, axial orientation and displacement. For comparison, the packing energies of the analogous assemblies of straight α-helices were also computed. Only those systems in which the chains were equivalent, i.e., related by line symmetry, were considered. The results indicate that for structures in which all the chains are equivalent the interchain packing energy favors the coiled coil arrangements.     

Effect of ions on the dielectric relaxation of DNA

The dielectric relaxation of DNA solutions has been investigated with and without extraneous ions covering a wide frequency range. The effect of monovalent ions such as Na, K, and Li as well as divalent ions such as Mg, Ca, and Hg have been included in the study. These ions are found to have a profound effect on the dielectric increment and the relaxation time without affecting the molecular dimension drastically. This dielectric effect is interpreted as indicating the importance of counterion fluctuation on the low frequency dielectric constant of DNA in solution. The effect of an organic ion, tetra-methylammoniun bromide, has also been studied. This ion has no noticeable effect. A simple theory is derived on the basis of a microscopic model to account for the effect of external ions on the dielectric behavior of solutions of DNA.     

Measurement and computation of the dipole moment of globular proteins III: Chymotrypsin

The dipole moments of alpha- and gamma-chymotrypsin are determined experimentally using the dielectric constant measuring method. The values thus obtained are compared with the results of the electric dichroism measurements for alpha-chymotrypsins by other investigators. The agreement is reasonably good, if not satisfactory. The cause of difference appears to be due to the difficulty of finding the correct internal field. The interaction between two neighboring dipoles is found to be a minor component of the local fields. Secondly, the dipole moment of alpha-chymotrypsin was computed using Protein Data Bases. The dipole moment of proteins consists of two major components, the moment due to fixed surface charges and the core moment due to polar chemical bonds. The method of calculation was described in detail in previous papers. The pK shifts of polar side chains were calculated using the methods of Tanford et al. and its modification by Warshel et al. The agreement between measured and calculated dipole moments is satisfactory.     

Influx of Ca ion in cultured excitable cells studied by fluorescence microscope imaging technique

The spatial distribution and temporal variation of intracellular Ca ion in differentiated Neuroblastoma-Glia Hybridoma 108–15 cells (NG108–15) were investigated using a fluorescence microscope imaging technique. Fura-2 was used as a probe. Electrical current pulses of 10–20 µA were applied to axons connecting to NG cells in order to elicit the influx of Ca ion. The concentration of intracellular Ca is usually 50–80 nM in NG cells in the resting state. Upon stimulation, the Ca level increases by a factor of 2–5. The entry of Ca⁺⁺ across cell membranes is followed by intracellular diffusion and the propagation of a wave front is clearly seen in digital images. The diffusion constant was calculated to be approximately 1.66×10^–6 cm²/sec. This value is about one-fifth of the free diffusion coefficient of Ca ion in aqueous solution (7.82 × 10^–6 cm²/sec). Cd ion, at the concentration of 1–2 mM, blocks the influx of Ca as expected whereas the influx is unaffected by TTX at the concentration of 0.1 – 0.2µM.     

Embryonic Development and Postnatal Changes in Free d-Aspartate and d-Serine in the Human Prefrontal Cortex

Abstract: We have analyzed free chiral amino acids (aspartate and serine) in the human frontal cortex at different ontogenic stages (from 14 weeks of gestation to 101 years of age) by HPLC with fluorometric detection after derivatization with N-tert -butyl-oxycarbonyl- l -cysteine and o -phthaldialdehyde. Exceptionally high levels of free d -aspartate and d -serine were demonstrated in the fetal cortex at gestational week 14. The ratios of d -aspartate and of d -serine to the total corresponding amino acids were also high, at 0.63 and 0.27, respectively. The concentration of d -aspartate dramatically decreased to a trace level by gestational week 41 and then remained very low during all postnatal stages. In contrast, the frontal tip contained persistently high levels of d -serine throughout embryonic and postnatal life, whereas the d -amino acid content in adolescents and aged individuals was about half of that in the fetuses. Because d -aspartate and d -serine are known to have selective actions at the NMDA-type excitatory amino acid receptor, the present data suggest that these d -amino acids might play a pivotal role in cerebral development and functions that are related to the NMDA receptor.