Reversible Mg2 Research Articles

Electrochemical intercalation of Mg2+ in 3D hierarchically porous magnesium cobalt silicate and its application as an advanced cathode material in rechargeable magnesium batteries

We firstly report the formation of 3D hierarchically porous MgCoSiO4 and the electrochemical intercalation of the bivalent cation Mg2+ in MgCoSiO4 with regard to its use as a cathode material in rechargeable magnesium batteries. Reversible Mg2+ intercalation can be demonstrated and the process is enhanced by the use of a novel 3D hierarchically porous architecture, consisting of a network of macropores with several nanometre wall and mesopores at the boundaries of grains or between grains. It is suggested that the interconnected wall structure, dual porosity and high surface area reduces the solid-state diffusion lengths for Mg diffusion, facilitates electrolyte penetration into particles and provides a large number of active sites for charge-transfer reactions.

Dynamics and function of compact nucleosome arrays

The packaging of eukaryotic DNA into chromatin sterically occludes polymerases, recombinases and repair enzymes. How chromatin structure changes to allow their actions is unknown. We constructed defined fluorescently labeled trinucleosome arrays, allowing analysis of chromatin conformational dynamics via fluorescence resonance energy transfer (FRET). The arrays undergo reversible Mg2+-dependent folding like that of longer arrays studied previously. We define two intermediate conformational states in the reversible folding of the nucleosome arrays, and characterize the microscopic rate constants. Nucleosome arrays are highly dynamic even when compact, undergoing conformational fluctuations on seconds to microseconds timescales. Compact states of the arrays allow binding to DNA within the central nucleosome via site exposure. Protein binding can also drive decompaction of the arrays. Thus, our results reveal multiple modes by which spontaneous chromatin fiber dynamics allows for the invasion and action of DNA processing protein complexes.

Electrochemical Intercalation of Mg2+ in Magnesium Manganese Silicate and Its Application as High-Energy Rechargeable Magnesium Battery Cathode

A study on electrochemical intercalation of bivalent cation Mg2+ in magnesium manganese silicate is reported. Reversible Mg2+ intercalation can be demonstrated and the process is enhanced by use of nanoscopic particles, resulted from a lower interfacial charge transfer resistance and a shorter solid-state diffusion distance of Mg2+ in the host. As a step toward novel rechargeable magnesium battery system, we have demonstrated the feasibility of the electrochemical oxidation, reduction, and cycling of magnesium manganese silicate. The results show that the silicate compound could be a good host for Mg2+ intercalation and a potential cathode material for high-energy rechargeable magnesium batteries.

Chromatin Structure in Granulocytes: A LINK BETWEEN TIGHT COMPACTION AND ACCUMULATION OF A HETEROCHROMATIN-ASSOCIATED PROTEIN (MENT)

To study the mechanism of heterochromatin formation in vertebrate cells, we isolated nuclei from chicken polymorphonuclear granulocytes and examined the chromatin organization. We found granulocyte chromatin to remain insoluble after nuclease digestion and to be resistant to swelling in low salt/high pH media. Both insolubility and resistance to swelling were lost after washing with 0.3 M NaCl, a procedure that released two abundant tissue-specific proteins from granulocyte nuclei. One of them (42 kDa) is identified as MENT, a protein previously shown to be associated with repressed chromatin from mature chicken erythrocytes. We show that MENT is immunolocalized in granulocyte heterochromatin, where it is one of the most abundant chromatin proteins ( approximately 2 molecules/200 base pairs of DNA). MENT is the first nuclear protein structurally related to the serine protease inhibitor family. The other abundant protein is similar to or identical with mim-1, a myeloid-specific protein that is known to be stored in cell granules and to associate with isolated nuclei. MENT (but not mim-1) binds chromatin and free DNA, and, at its physiological protein/DNA ratio, enhances compaction and the reversible Mg2+-dependent self-association of nucleosome arrays. MENT appears to promote the formation of heterochromatin by acting as a "glue" within and between chains of nucleosomes.

Effect of temperature on the mechanism of actin polymerization.

The rate of the Mg2+-induced polymerization of rabbit skeletal muscle G-actin has been measured as as function of temperature at pH 8 by using various concentrations of Mg2+, Ca2+, and G-actin. A polymerization mechanism similar to that proposed at this pH [Frieden, C. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 6513-6517] was found to fit the data from 10 to 35 degrees C. From the kinetic data, no evidence for actin filament fragmentation was found at any temperature. Dimer formation is the most temperature-sensitive step, with the ratio of forward and reverse rate constants changing 4 orders of magnitude from 10 to 35 degrees C. Over this temperature change, all other ratios of forward and reverse rate constants change 7-fold or less, and the critical concentration remains nearly constant. The reversible Mg2+-induced isomerization of G-actin monomer occurs to a greater extent with increasing temperature, measured either by using N-(iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine-labeled actin or by simulation of the full-time course of the polymerization reaction. This is partially due to Mg2+ binding becoming tighter, and Ca2+ binding becoming weaker, with increasing temperature. Elongation rates from the filament-pointed end, determined by using actin nucleated by plasma gelsolin, show a temperature dependence slightly larger than that expected for a diffusion-limited reaction.

Characterization and properties of the pyruvate phosphorylation system of Acetobacter xylinum.

The enzyme responsible for the direct phosphorylation of pyruvate during gluconeogenesis in Acetobacter xylinum has been purified 46-fold from ultrasonic extracts and freed from interfering enzyme activities. The enzyme was shown to catalyze the reversible Mg(2+) ion-dependent conversion of equimolar amounts of pyruvate, adenosine triphosphate (ATP), and orthophosphate (P(i)) into phosphoenolpyruvate (PEP), adenosine monophosphate (AMP), and pyrophosphate (PP). The optimal pH for PEP synthesis was pH 8.2; for the reversal it was pH 6.5. The ratio between the initial rates of the reaction in the forward and reverse directions was 5.1 at pH 8.2 and 0.45 at pH 6.5. The apparent K(m) values of the components of the system in the forward reaction were: pyruvate, 0.2 mm; ATP, 0.4 mm; P(i), 0.8 mm; Mg(2+), 2.2 mm; and for the reverse reaction: PEP, 0.1 mm; AMP, 1.6 mum; PP, 0.067 mm; Mg(2+), 0.87 mm. PEP formation was inhibited by AMP and PP. The inhibition by AMP was competitive with regard to ATP (K(i) = 0.2 mm). The reverse reaction was inhibited competitively by ATP and noncompetitively by pyruvate. The enzyme was strongly inhibited by p-hydroxymercuribenzoate. The inhibition was reversed by dithiothreitol and glutathione. The properties of the enzyme are discussed in relation to the regulation of the opposing enzymatic activities involved in the interconversion of PEP and pyruvate in A. xylinum.