Acceleration of impurity ions in the coulomb explosion of a relativistic spherical cluster with a complex ion composition

A semi-analytical model of the acceleration of light impurity ions to relativistic energies in the Coulomb explosion of a spherically symmetric homogeneous microtarget (cluster) consisting of ions of two types has been proposed. The spatiotemporal and spectral characteristics of accelerated impurity ions, which have a quasi-monochromatic spectrum, have been determined. The properties of high-energy impurity ions have been studied as functions of the total charge of the cluster and its ion composition.     

Modeling of isotopomeric cluster of the molecular ion

The occurrence of poly-isotopic elements in a molecule or ion can result in complex isotopomeric cluster of an ion. The “isotopomer” better and correctly indicates different isotopic compositions of a molecule (compound) or ion and not a single atom. The ions of organic compounds show in accurate mass spectra single, isolated peaks or narrow sub-clusters regardless of their molecular masses. The occurrence of a PIE makes the molecular ion cluster more complex and significantly influences the location of the most abundant peak and the form of the cluster. The present study is an attempt at answering the following question: what is the mechanism of the molecular ion’s isotopomeric cluster formation and is it step-by-step predictable? The accurate mass-resolved isotopomer cluster can be predicted from accurate masses and abundances of the stable isotopes. The cluster consists of several sub-patterns, each of which is composed of near signals (at the same nominal m/z). The range of the sub-cluster usually does not exceed 0.005 u. The low-resolution cluster can be predicted from the high-resolution pattern by addition of all peaks occurring over a given narrow mass range (m/z - 0.5; m/z+0.49). Surprisingly, predicting the accurate mass cluster is simpler than predicting the low-resolution one. A compliance of the model results with the experimental ones suggests a correct prediction. Figure: Isotopomeric genesis of the mass spectral cluster.

Effect of microfield fluctuations on Coulomb collisions

The effect of plasma microfields on Coulomb collisions between the particles is considered. It is shown that perturbations from other particles insignificantly affect the frequency of short-range collisions. The results of calculating the pair correlation function of the particles in a plasma for distances much shorter than the interparticle distance agree well with predictions of the binary theory.     

Trapping single ions inside single ion channels.

Single Ca++-activated K+ channels from rat muscle plasma membranes are inhibited by Ba++. A single Ba++ entering the channel's conduction pore induces a long-lived blocked state. This study employs Ba++ as a probe of the channel's conduction pathway to show that the channel can be forced to close with a single Ba++ ion inside the pore. A Ba++ ion inside the closed channel is trapped and cannot escape until the channel opens. The results demonstrate that in the channel's closed state, the cytoplasmic side of the conduction pore is obstructed to the passage of ions.     

Mirror image mutations reveal the significance of an intersubunit ion cluster in the stability of 3-isopropylmalate dehydrogenase

The comparison of the three-dimensional structures of thermophilic (Thermus thermophilus) and mesophilic (Escherichia coli) 3-isopropylmalate dehydrogenases (IPMDH, EC 1.1.1.85) suggested that the existence of extra ion pairs in the thermophilic enzyme found in the intersubunit region may be an important factor for thermostability. As a test of our assumption, glutamine 200 in the E. coli enzyme was turned into glutamate (Q200E mutant) to mimic the thermophilic enzyme at this site by creating an intersubunit ion pair which can join existing ion clusters. At the same site in the thermophilic enzyme we changed glutamate 190 into glutamine (E190Q), hereby removing the corresponding ion pair. These single amino acid replacements resulted in increased thermostability of the mesophilic and decreased thermostability of the thermophilic enzyme, as measured by spectropolarimetry and differential scanning microcalorimetry.     

Divalent ion trapping inside potassium channels of human T lymphocytes

Using the patch-clamp whole-cell recording technique, we investigated the influence of external Ca2+, Ba2+, K+, Rb+, and internal Ca2+ on the rate of K+ channel inactivation in the human T lymphocyte-derived cell line, Jurkat E6-1. Raising external Ca2+ or Ba2+, or reducing external K+, accelerated the rate of the K+ current decay during a depolarizing voltage pulse. External Ba2+ also produced a use-dependent block of the K+ channels by entering the open channel and becoming trapped inside. Raising internal Ca2+ accelerated inactivation at lower concentrations than external Ca2+, but increasing the Ca2+ buffering with BAPTA did not affect inactivation. Raising [K+]o or adding Rb+ slowed inactivation by competing with divalent ions. External Rb+ also produced a use-dependent removal of block of K+ channels loaded with Ba2+ or Ca2+. From the removal of this block we found that under normal conditions approximately 25% of the channels were loaded with Ca2+, whereas under conditions with 10 microM internal Ca2+ the proportion of channels loaded with Ca2+ increased to approximately 50%. Removing all the divalent cations from the external and internal solution resulted in the induction of a non-selective, voltage-independent conductance. We conclude that Ca2+ ions from the outside or the inside can bind to a site at the K+ channel and thereby block the channel or accelerate inactivation.     

Parvalbumins. Distribution and physical state inside the muscle cell.

Single skinned muscle fibres (frog) have been submitted to double Ouchterlony immunodiffusion assays with antibodies directed against the two species of frog parvalbumins. The antigenic material which diffuses out of each fibre contains the two parvalbumins. Their presence in each cell is thus demonstrated. The amount of parvalbumins having diffused out of the fibre has been quantified. It corresponds to the parvalbumin content of the cell. This implies that these proteins are freely soluble in the muscle sarcoplasm.     

Enzyme immobilization by the coulomb force

A new immobilization technique has been developed. It involves immobilizing enzymes on a porous polytetrafluoroethylene membrane with a nonporous polyurethane coat by the use of an electrostatic force, i.e. the Coulomb force. The immobilized enzyme can be recovered by supplying a reversed electrical potential. The reaction characteristics of the immobilized amyloglucosidase were studied using maltose as a substrate. The Michaelis constant becomes larger than that of the native enzyme, and depends on the electrical potential gradient in the solution.     

Distribution of the vanG-like gene cluster in Clostridium difficile clinical isolates

Treatment of Clostridium difficile infections generally requires cessation of their causative antibiotic and subsequent administration of metronidazole or vancomycin. Intriguingly, the genome of C. difficile 630 contains a cryptic gene cluster homologous to the vanG-type operon of Enterococcus faecalis BM4518. We detected this cluster by PCR in 35 out of 41 clinical isolates, confirming its large prevalence in this species. The cluster was found to be located in a unique locus. Comparison of this locus with that of strains devoid of the vanG-like cluster indicated that acquisition of the gene cluster occurred in a perfect 19-bp inverted repeat, in the absence of a detectable mobile structure.     

Distribution of the lithium ion in endocrine organs of the rat

Lithium ions accumulated consistently in the pituitary and thyroid of rats at concentrations significantly greater than in plasma. There was also a significant, although lower, accumulation of Li⁺ in the adrenal gland. No accumulation of lithium ion was noted in the testis or in the ovary. The possible significance of these findings with regard to some of the side effects of lithium carbonate treatment is discussed.     

Distribution of proteins inside polyelectrolyte microcapsules depend on pH of medium

Distribution of bovine serum albumin and ferritin inside polyelectrolyte microcapsules was studied by transmission electron and confocal microscopy at the pH range 2-5. It was estimate that protein's distribution depends on isoelectric point (pI) and first polyelectrolyte used for preparation of capsule shell. So peptide is placed in the bulk of capsule if pH values of medium are lower isoelectric point of protein and polycation was used as a first polyelectrolyte layer. If the first polyelectrolyte was polyanion, the protein is located near internal surface of the shell. The protein is situated near internal surface of the shell for both polyelectrolytes when pH is equal to pI.     

Bistable regulation of integrin adhesiveness by a bipolar metal ion cluster

Integrin alpha(4)beta(7) mediates rolling adhesion in Ca(2+) and Ca(2+) + Mg(2+), and firm adhesion in Mg(2+) and Mn(2+), mimicking the two key steps in leukocyte accumulation in inflamed vasculature. We mutated an interlinked linear array of three divalent cation-binding sites present in integrin beta-subunit I-like domains. The middle, metal ion-dependent adhesion site (MIDAS) is required for both rolling and firm adhesion. One polar site, that adjacent to MIDAS (ADMIDAS), is required for rolling because its mutation results in firm adhesion. The other polar site, the ligand-induced metal binding site (LIMBS), is required for firm adhesion because its mutation results in rolling. The LIMBS mediates the positive regulatory effects of low Ca(2+) concentrations, whereas the ADMIDAS mediates the negative regulatory effects of higher Ca(2+) concentrations, which are competed by Mn(2+). The bipolar sites thus stabilize two alternative phases of adhesion.