Like-charged polyelectrolytes can attract and condense into compact ordered states via counterion-mediated interactions (Gelbart et al 2000 Phys. Today 53 38–44). Recent examples include DNA toroids and F-actin bundles. We have investigated the structure and dynamics of condensed divalent ions within F-actin polyelectrolyte bundles. Using synchrotron x-ray diffraction, the structural organizati...

Annexins belong to a family of Ca2+- and phospholipid-binding proteins that can mediate the aggregation of granules and vesicles in the presence of Ca2+. We have studied the effects of different divalent metal ions on annexin-mediated aggregation of liposomes using annexins isolated from rabbit liver and large unilamellar vesicles prepared from soybean asolectin II-S. In the course of these stu...

The aim of this study was to investigate the effect of divalent metal ions (Ca, Mg(2+) , and Zn(2+) ) on the stability of oxytocin in aspartate buffer (pH 4.5) and to determine their interaction with the peptide in aqueous solution. Reversed-phase high-performance liquid chromatography and high-performance size-exclusion chromatography measurements indicated that after 4 weeks of storage at 55°...

The propert ies of rumen urease were studied. In the absence of high concentrations of dithiothreitol enzyme activity was rapidly lost; in its presence, the enzyme could be solubilized and purified in high yield. Maximum activity was observed between pH 7 and 8.5. The Km for urea with partially purified enzyme was .004 M with Vmax of 300 to 400 #moles/mg/hr. No divalent metal ion requirement or...

The DNA cleavage reaction of human topoisomerase IIalpha is critical to all of the physiological and pharmacological functions of the protein. While it has long been known that the type II enzyme requires a divalent metal ion in order to cleave DNA, the role of the cation in this process is not known. To resolve this fundamental issue, the present study utilized a series of divalent metal ions ...

The fusogenic activity of plant Golgi membranes was studied in a cell-free system by assaying lipid mixing and content leakages of fluorescence probes. Golgi membranes from mung bean (Vigna radiata L.) hypocotyl cells fused to liposomes in the absence of any cytosolic proteins and nucleotides. It was demonstrated that the fusion was mediated by integral membrane protein(s), and was influenced b...

Hydrogelation behavior of two amino-terpyridine ligands in the presence of divalent metal ions in water was studied in detail. The effect of ligand structure and different counter anions on the gel morphologies was also explored.

The voltage dependence of the voltage clamp responses of myelinated nerve fibers depends on the concentration of divalent cations and of hydrogen ions in the bathing medium. In general, increases of the [Ca], [Ni], or [H] increase the depolarization needed to elicit a given response of the nerve. An e-fold increase of the [Ca] produces the following shifts of the voltage dependence of the param...

Intermediate filament networks in the cytoplasm and nucleus are critical for the mechanical integrity of metazoan cells. However, the mechanism of crosslinking in these networks and the origins of their mechanical properties are not understood. Here, we study the elastic behavior of in vitro networks of the intermediate filament protein vimentin. Rheological experiments reveal that vimentin net...

Lanthanides in compounds can adopt the tetravalent [Xe]4f n−1 (like Ce4+, Pr4+, Tb4+), the trivalent [Xe]4f n (all lanthanides), or the divalent [Xe]4f n+1 configuration (like Eu2+, Yb2+, Sm2+, Tm2+). The 4f -electron binding energy depends on the charge Q of the lanthanide ion and its chemical environment A. Experimental data on three environments (i.e., the bare lanthanide ions where A = vacu...