The possible role of tightly bound adenine nucleotides in oxidative and photosynthetic phosphorylation.

The tightly bound nucleotides of the beff-heart mitochondrial ATPase are released during cold inactivation followed by ammonium sulfate precipitation. During incubation at 0 degrees C the sedimentation coefficient (S20W) of the ATPase first declines from 12.1S to 9S. Prolonged incubation or precipitation with ammonium sulfate leads to dissociation of the 9S component into subunits with S20W of 3.5S. The 9S component still bears bound nucleotides which exchange more extensively and rapidly with added nucleotides than those bound to the active 12.1S component. The bound nucleotides are lost when the 9S form dissociates into the smaller subunits. Thus, firm binding of nucleotides is a property of the quarternary structure of the enzyme. The exchangeability of the nucleotides bound to the ATPase of chloroplast membranes is greatly increased in membranes illuminated in the presence of pyocyanine. Pi can exchange into both the beta and gamma positions of the bound nucleotides when the membranes are energized in the presence of Mg2+. The exchange of the nucleotides and the incorporation of Pi are insensitive to the inhibitor Dio-9 but are inhibited by the uncoupler S13. This inhibition by S13 parallels that of the inhibition of photosynthetic phosphorylation. These findings are discussed with regard to our hypothesis that electron transfer causes release of preformed tightly bound ATP from the ATPase by inducing a conformational change.     

A comparison of the effect of rare earth vs Si site doping on the conductivities of apatite-type rare earth silicates

Apatite-type lanthanum silicate (La_9.33Si₆O₂₆) has been attracting significant recent interest due to its high oxide ion conductivity. In this paper, synthesis and conductivity data for a range of doped samples (Mg, Ca, Sr, Ba, B, Ga and Zn) are reported, in particular, to compare the effect of rare earth vs Si site doping. The results show that Ga, B and Zn favour substitution on the Si site, while Ca, Sr and Ba favour La-site substitution. Mg is shown to be an ambi-site dopant, substituting on either site depending on the starting composition. The samples doped on the Si site show higher conductivities than comparable samples doped on the La site, providing further support for the importance of the silicate network in the conduction process, as initially predicted by atomistic modelling studies. For Ga doping on the Si site, the effect of varying the rare-earth size on the conductivities is also reported.     

Futtermittel

Ohne Zusammenfassung     

A Tamao–Fleming oxidation route to dipeptides bearing N,O-acetal functionality

Tamao–Fleming oxidation of the N-dimethylphenylsilylmethyl group linked to the nitrogen of a peptide bond enables access to dipeptide N,O-acetal functionality. The N-silylmethyl functionality serves as a latent form of the N,O-acetal which is revealed after peptide bond construction.     

Effective Debye length in closed nanoscopic systems: a competition between two length scales

The Poisson-Boltzmann equation (PBE) is widely employed in fields where the thermal motion of free ions is relevant, in particular in situations involving electrolytes in the vicinity of charged surfaces. The applications of this non-linear differential equation usually concern open systems (in osmotic equilibrium with an electrolyte reservoir, a semi-grand canonical ensemble), while solutions for closed systems (where the number of ions is fixed, a canonical ensemble) are either not appropriately distinguished from the former or are dismissed as a numerical calculation exercise. We consider herein the PBE for a confined, symmetric, univalent electrolyte and quantify how, in addition to the Debye length, its solution also depends on a second length scale, which embodies the contribution of ions by the surface (which may be significant in high surface-to-volume ratio micro- or nanofluidic capillaries). We thus establish that there are four distinct regimes for such systems, corresponding to the limits of the two parameters. We also show how the PBE in this case can be formulated in a familiar way by simply replacing the traditional Debye length by an effective Debye length, the value of which is obtained numerically from conservation conditions. But we also show that a simple expression for the value of the effective Debye length, obtained within a crude approximation, remains accurate even as the system size is reduced to nanoscopic dimensions, and well beyond the validity range typically associated with the solution of the PBE.     

Free-solution electrophoresis of DNA modified with drag-tags at both ends

In end-labeled free-solution electrophoresis (ELFSE), DNA molecules are labeled with a frictional modifier or "drag-tag", allowing their size-based electrophoretic separation in free solution. Among the interesting observations from early work with dsDNA using streptavidin as a drag-tag was that the drag induced by including a streptavidin label at both ends was significantly more than double that from a single streptavidin (Heller, C. et al.., J. Chromatogr. A 1998, 806, 113-121). This finding was assumed to be in error, and subsequent work focused on experiments in which only a single drag-tag is appended to one end of the DNA molecule. Recent theoretical work (McCormick, L. C., Slater, G. W., Electrophoresis 2005, 26, 1659-1667) has examined the contribution of end-effects to the free-solution electrophoretic mobility of charged-uncharged polymer conjugates, reopening the question of enhanced drag from placing a drag-tag at both ends. In this study, this effect is investigated experimentally, using custom-synthesized ssDNA oligonucleotides allowing the attachment of drag-tags to one or both ends, as well as dsDNA PCR products generated with primers appropriate for the attachment of drag-tags at one or both ends. A range of sizes of drag-tags are used, including synthetic polypeptoid drag-tags as well as genetically engineered protein polymer drag-tags. The enhanced drag arising from labeling both ends has been confirmed, with 6-9% additional drag for the ssDNA and 10-23% additional drag for the dsDNA arising from labeling both ends than would be expected from simply doubling the size of the drag-tag at one end. The experimental results for ssDNA labeled at both ends are compared to the predictions of the recent theory of end-effects, with reasonably good quantitative agreement. These experimental findings demonstrate the feasibility of enhancing ELFSE separations by labeling both ends of the DNA molecule, leading to greater resolving power and a wider range of applications for this technique.     

Incidence and properties of nanoscale defects in silicalite

Crystal intergrowths are predicted to form more readily than other extended defects in a model zeolite membrane and cause a reduction in molecular flux.