Charge transport in B-carotene

The absorption currents in the ‘cis-trans’ isomeric forms of β-carotene glass were studied over a wide range of temperature and field. Limited observations of the absorption currents were also made with different sample thicknesses and electrode materials. The results indicate that the low temperature absorption current (<273K) may be due to a dipolar mechanism with a distribution of relaxation times whereas the absorption current in the high temperature range (≃273K<T<333K) may be adequately explained by a hopping mechanism of charge carriers through the localized states distributed by the bulk.     

Characteristics of the heterogeneity of the physical properties of the lipid phase of synaptic membranes from the rat brain using the fluorescent probe pyrene

A theoretical analysis of the dependence of pyrene excimerization on its concentration in biological membranes was carried out. It was shown that in synaptic membranes the concentration dependencies of pyrene excimerization parameter upon direct stimulation appear as nonlinear, thus being reflective of the heterogeneity of physical properties of the lipid phase. Upon pyrene excitation at the expense of the energy transfer from tryptophanyl residues the dependence is linear, which points to the homogeneity of the anular lipid pool. It was assumed that a comparison of microviscosity of the anular and bilayer lipids requires independent measurements of the coefficient of the probe distribution between the lipids or of the anular lipid content in the membrane.     

Relative Efficiencies of Plasma Catechol Levels and Ratios for Neonatal Diagnosis of Menkes Disease

Background Menkes disease is an X-linked recessive neurodevelopmental disorder resulting from mutation in a copper-transporting ATPase gene. Menkes disease can be detected by relatively high concentrations of dopamine (DA) and its metabolites compared to norepinephrine (NE) and its metabolites, presumably because dopamine-beta-hydroxylase (DBH) requires copper as a co-factor. The relative diagnostic efficiencies of levels of catechol analytes, alone or in combination, in neonates at genetic risk of Menkes disease have been unknown. Methods Plasma from 44 at-risk neonates less than 30 days old were assayed for DA, NE, and other catechols. Of the 44, 19 were diagnosed subsequently with Menkes disease, and 25 were unaffected. Results Compared to unaffected at-risk infants, those with Menkes disease had high plasma DA (P < 10⁻⁶) and low NE (P < 10⁻⁶) levels. Considered alone, neither DA nor NE levels had perfect sensitivity, whereas the ratio of DA:NE was higher in all affected than in all unaffected subjects (P = 2 × 10⁻⁸). Analogously, levels of the DA metabolite, dihydroxyphenylacetic acid (DOPAC), and the NE metabolite, dihydroxyphenylglycol (DHPG), were imperfectly sensitive, whereas the DOPAC:DHPG ratio was higher in all affected than in all unaffected subjects (P = 2 × 10⁻⁴). Plasma dihydroxyphenylalanine (DOPA) and the ratio of epinephrine (EPI):NE levels were higher in affected than in unaffected neonates (P = 0.0015; P = 0.013). Conclusions Plasma DA:NE and DOPAC:DHPG ratios are remarkably sensitive and specific for diagnosing Menkes disease in at-risk newborns. Affected newborns also have elevated DOPA and EPI:NE ratios, which decreased DBH activity alone cannot explain.     

Multipole effects on the dielectrophoretic force in an ‘isomotive’ field

The derivation of the isomotive field geometry for cieiertrophoresis assumes that the field is uniform relative to the timensions of the particie of interest. For this situation the particle may be modelled as a point dipole.A more rigorous attempt has been made in this study to inolude contributions due to multiple effects. The error introduced by the tinite nonuniformity is investigated and presented in a generai analytical torm. A numerical result, calculated for the case of isomotive field chamber. devoia of edge effects, indicated that contributions due to multipole effects are negligible outside of a region within a few particle radii about the origin.     

A model of cooperative rearrangements of biological membranes without changes in the affinity of receptor binding centers

A mathematical model is proposed for cooperative rearrangements induced by specific ligand in certain biomembrane domains. They are considered as the N-valent receptors undergoing rearrangement when n less than or equal to N ligand-binding receptor sites are occupied. The model predicts distinct sigmoidal dependence for change of some structural parameter on ligand concentration when the receptor site-ligand affinity remains constant as binding rises (positive cooperativity is absent).     

The conflicting action of low and high doses of ozone on the reproductive capacity and respiratory activity of Candida utilis yeast cells

Different doses of ozone were shown either to stimulate (1-2 x 10(8) molecules O3/cell) or inhibit (1 x 10(9) molecules O3/cell) respiration and reproduction of C. utilis yeast. The observed changes were preserved for several hours after treatment with ozone. Possible role of structural rearrangements of cell membranes in the ozone-induced effects has been discussed.     

Protein damage after treatment with ozone of protoplasts and isolated E. coli membranes

The features of ozone-induced damage of E. coli plasma membrane proteins are investigated. A conclusion is made that protein fluorescence quenching is connected with modification of amino acid residues in the vicinity of tryptophane residues. Such modification may be a consequence of reaction with either ozone itself or products of its interaction with membrane lipids and/or proteins. The suggestion of Goldstein and McDonagh that ozone has a predilection for more hydrophilical membrane domains is confirmed. The data obtained are in agreement with a supposition about the leading role of proteins in deleterious action of ozone on cells.     

Dynamic dielectrophoretic levitation of living individual cells

The levitation of lone live cells by means of dielectrophoretic force provides a means of determining the relative polarization of the cells and their aqueous support medium. When done over a range of frequencies, a spectrum of dielectric (polarization) responses is obtained which serves to characterize a single living ell. In this manner, individual cells of several microorganisms,Saccharomyces cerevisiae andNetrium digitus, were investigated in the frequency range 10² to 10⁶ Hz. These and related prior studies showed that the positive dielectrophoresis, i.e. where the suspended particle has a greater net polarization than the suspending medium, can be — used to show subtle differences between species, and even between cells of the same culture when using this technique.