F0 cysteine,bCys21, in the Escherichia coli ATP synthase is involved in regulation of potassium uptake and molecular hydrogen production in anaerobic conditions

The single cysteine in the b subunit of the membranous F₀ sector and the 19 cysteines in extramembranous F₁ sector of the Escherichia coli ATP synthase were replaced by alanine. When cells were grown under anaerobic conditions on glucose, the k _cat for ATP hydrolysis of membrane vesicles containing the bCys21Ala mutant enzyme, but not enzymes with other cysteine replacements, was lower, while ATP-driven H⁺ pumping was unchanged. However, the ATP-dependent increase in the number of accessible thiol groups in membrane vesicles was negated. Furthermore, K⁺ uptake and molecular hydrogen production by whole cells and protoplasts was greatly decreased. These results indicate a role for the F₀ subunit bCys21 in the functionality of F₀F₁ and coupling to other membranous activities under fermentative conditions.     

Increase in temperature induces the Z to B transition of poly[d(G-C)] in water-ethanol solution

An increase in temperature from 20 to 50° C results in the complete transition from the Z to B form of poly(d(G-C)], dissolved in a 55% ethanol-water solution. The transition is fully reversible and displays a slow kinetics. The transition profiles for the free polynucleotide and for that in the presence of ethidium bromide, which is known to stabilize the B form, are obtained by circular dichroism. Based on these data the enthalpy value for the B-Z transition in our conditions is estimated to be ΔH_BZ = ?0.7 $\text{kcal}\text{mol}$.     

Influence of ionic strength on Hoechst 33258 binding with DNA

The binding of Hoechst 33258 with DNA at various ionic strengths of solution and different ligand concentrations has been investigated. Existence of more than one type of interactions of Hoechst 33258 with DNA has been revealed, which were very sensitive to the ionic strength. Hoechst 33258 doesn't show specificity to AT sequences of DNA at low ionic strength. High affinity binding mode becomes obvious at high ionic strength. The values of binding constants and binding site sizes for revealed strong and weak interactions have been determined.     

The roles of hydrogenases 3 and 4, and the F0F1-ATPase, in H2 production by Escherichia coli at alkaline and acidic pH

The hyc operon of Escherichia coli encodes the H2-evolving hydrogenase 3 (Hyd-3) complex that, in conjunction with formate dehydrogenase H (Fdh-H), constitutes a membrane-associated formate hydrogenlyase (FHL) catalyzing the disproportionation of formate to CO2 and H2 during fermentative growth at low pH. Recently, an operon (hyf) encoding a potential second H2-evolving hydrogenase (Hyd-4) was identified in E. coli. In this study the roles of the hyc- and hyf-encoded systems in formate-dependent H2 production and Fdh-H activity have been investigated. In cells grown on glucose under fermentative conditions at slightly acidic pH the production of H2 was mostly Hyd-3- and Fdh-H-dependent, and Fdh-H activity was also mainly Hyd-3-dependent. However, at slightly alkaline pH, H2 production was found to be largely Hyd-4, Fdh-H and F0F1-ATPase-dependent, and Fdh-H activity was partially dependent on Hyd-4 and F0F1-ATPase. These results suggest that, at slightly alkaline pH, H2 production and Fdh-H activity are dependent on both the F0F1-ATPase and a novel FHL, designated FHL-2, which is composed of Hyd-4 and Fdh-H, and is driven by a proton gradient established by the F0F1-ATPase.     

Hydrogenase 3 but not hydrogenase 4 is major in hydrogen gas production by Escherichia coli formate hydrogenlyase at acidic pH and in the presence of external formate

Fermenting Escherichia coli is able to produce formate and molecular hydrogen (H2) when grown on glucose. H2 formation is possessed by two hydrogenases, 3 (Hyd-3) and 4 (Hyd-4), those, in conjunction with formate dehydrogenase H (Fdh-H), constitute distinct membrane-associated formate hydrogenylases. At slightly alkaline pH (pH 7.5), the production of H2 was found to be dependent on Hyd-4 and the F0F1-adenosine triphosphate (ATPase), whereas external formate increased the activity of Hyd-3. In this study with cells grown without and with external formate, H2 production dependent on pH was investigated. In both types of cells, H2 production was increased after lowering of pH. At acidic pH (pH 5.5), this production became insensitive either to N,N'-dicyclohexylcarbodiimide or to osmotic shock and it became largely dependent on Fdh-H and Hyd-3 but not Hyd-4 and the F0F1-ATPase. The results indicate that Hyd-3 has a major role in H2 production at acidic pH independently on the F0F1-ATPase.     

95 Orientational ordering of short DNA fragments in the polymer matrix

As a vital part of modern nanotechnology, nanofabrication aims to develop nanoscale components and nanomaterials in large quantities at relatively low cost. The promising strategy is the bottom-up self-assembly techniques of chemical assembly and molecular recognition to bring together individual atoms, molecules, or supramolecular building blocks to form useful constructs. The DNA-DNA self-assembly seems to be the key point regulating the polymer composites formation. We address the mixture of a flexible polymer with short double-strand DNA fragments, where the persistence length is in comparable with the contour length of the molecule. We investigate the conditions affecting the orientational order formation of short double-strand DNA fragments, immersed in the flexible polymer. It is shown that short double-strand DNA fragments exhibit the formation of a liquid crystalline ordered phase, in dependence on the value of the Flory–Huggins parameter, aspect ratio , and the attraction energy (Mamasakhlisov et al., 2009; Todd et al., 2008) of the double strand DNA molecules and volume fraction of polymer.     

Correlation Between Endodontic Broken Instrument and Nickel Level in Urine

This study aims to evaluate the correlation between the presences of separated endodontic instrument inside the dental canal and the nickel (Ni) level in the urine samples of subjected patients. Same-gendered and near-aged participants were selected and were instructed to collect their urine in sterile nickel-free plastic containers. The procedures were carried out in the office, and samples were stored in low-temperature cooler for 1 day and then they were transferred to the laboratory for electrothermal atomic absorption spectrometry. The level of Ni was measured and the correlation coefficient was calculated. Data were analyzed using t tests, Pearson’s correlation coefficients, and linear regression analysis, at a level of significance P?<?0.05. The statistical analysis has showed significant difference in Ni level between endodontic and control groups (P?<?0.05). There was no correlation between Ni level in urine and the age or time period of broken instrument inside the canal; however, Ni level of urine and the age of participants in experimental group has demonstrated a positive correlation. The amount of Ni element can be increased in the urine of patients who have experienced broken endodontic instrument inside the dental canal. However, there is no positive correlation between the remaining pieces of instruments inside the canal and the elevation of nickel amount in urine during the tested time period. This issue suggested that the aging of remaining broken instrument inside the canal does not show any remarkable concern regarding the Ni elevation in the urine excreted by an individual.