Spectroscopic and computational studies of nitrite reductase: proton induced electron transfer and backbonding contributions to reactivity.
A combination of spectroscopy and DFT calculations has been used to define the geometric and electronic structure of the nitrite bound type 2 (T2) copper site at high and low pH in nitrite reductase from Rhodobacter sphaeroides. At high pH there is no electron transfer from reduced type 1 (T1) to the nitrite bound T2 copper, while protonation triggers T1 --> T2 electron transfer and generation of NO. The DFT calculated reaction coordinate for the N-O bond cleavage in nitrite reduction by the reduced T2 copper suggests that the process is best described as proton transfer triggering electron transfer. Bidentate nitrite binding to copper is calculated to play a major role in activating the reductive cleavage of the nitrite bond through backbonding combined with stabilization of the (-)OH product by coordination to the Cu(2+).

title: Spectroscopic and electronic structure studies of phenolate Cu(II) complexes: phenolate ring orientation and activation related to cofactor biogenesis.
abstract: A combination of spectroscopies and DFT calculations have been used to define the electronic structures of two crystallographically defined Cu(II)-phenolate complexes. These complexes differ in the orientation of the phenolate ring which results in different bonding interactions of the phenolate donor orbitals with the Cu(II), which are reflected in the very different spectroscopic properties of the two complexes. These differences in electronic structures lead to significant differences in DFT calculated reactivities with oxygen. These calculations suggest that oxygen activation via a Cu(I) phenoxyl ligand-to-metal charge transfer complex is highly endergonic (>50 kcal/mol), hence an unlikely pathway. Rather, the two-electron oxidation of the phenolate forming a bridging Cu(II) peroxoquinone complex is more favorable (11.3 kcal/mol). The role of the oxidized metal in mediating this two-electron oxidation of the coordinated phenolate and its relevance to the biogenesis of the covalently bound topa quinone in amine oxidase are discussed.

title: Existence of cholinephosphotransferase in mitochondria and microsomes of liver and lung of guinea pig and rat
abstract: We reported earlier on the occurrence of cholinephosphotransferase in the mitochondria of guinea pig lung. In order to determine whether organ and/or species specificities exist in regard to the cholinephosphotransferase activity in mitochondria, we have compared the subcellular distribution of the enzyme in the liver and lungs of rats and guinea pigs. Even though the activity of the enzyme was higher in microsomes than it was in mitochondria, the mitochondrial activity was authentic in both tissues of both species. The authenticity of mitochondrial activity was established by marker enzyme studies and ultrastructural examination of mitochondrial preparations.

title: Acaricidal properties of Ricinus communis leaf extracts against organophosphate and pyrethroids resistant Rhipicephalus (Boophilus) microplus.
abstract: Indian cattle ticks have developed resistance to commonly used acaricides and an attempt has been made to formulate an ecofriendly herbal preparation for the control of acaricide resistant ticks. A 95% ethanolic extract of Ricinus communis was used to test the efficacy against reference acaricide resistant lines by in vitro assay. In in vitro assay, the extract significantly affects the mortality rate of ticks in dose-dependent manner ranging from 35.0 ± 5.0 to 95.0 ± 5.0% with an additional effect on reproductive physiology of ticks by inhibiting 36.4-63.1% of oviposition. The leaf extract was found effective in killing 48.0, 56.7 and 60.0% diazinon, deltamethrin and multi-acaricide resistant ticks, respectively. However, the cidal and oviposition limiting properties of the extract were separated when the extract was fractionated with hexane, chloroform, n-butanol and water. The HPTLC finger printing profile of R. communis leaf extract under λ(max.) - 254 showed presence of quercetin, gallic acid, flavone and kaempferol which seemed to have synergistic acaricidal action. In vivo experiment resulted in 59.9% efficacy on Ist challenge, however, following 2nd challenge the efficacy was reduced to 48.5%. The results indicated that the 95% ethanolic leaf extract of R. communis can be used effectively in integrated format for the control of acaricide resistant ticks.

title: CK2 constitutively associates with and phosphorylates chicken erythroid ankyrin and regulates its ability to bind to spectrin
abstract: Previous analyses have shown that the phosphorylation state of chicken erythroid ankyrin regulates its association with the spectrin cytoskeleton in vivo. Treatment of erythroid cells with serine and threonine phosphatase inhibitors stimulates the hyperphosphorylation of ankyrin and its dissociation from spectrin. In this study, we demonstrate that a kinase that directs the phosphorylation of ankyrin in vivo coprecipitates with ankyrin-containing complexes and has properties identical to CK2. Studies using CK2-specific inhibitors have indicated that all of the phosphorylation events associated with erythroid ankyrin in vivo are CK2 dependent. Furthermore, inhibitor studies combined with in vitro binding analyses have indicated that the phosphorylation of erythroid ankyrin by CK2 regulates its ability to associate with spectrin. Additional analyses revealed that CK2 coprecipitates with ankyrin-3-containing complexes isolated from Madin Darby canine kidney epithelial cells and phosphorylates this epithelial ankyrin isoform in vivo. These results are the first demonstration of a kinase constitutively associating with the ankyrin-spectrin cytoskeleton in erythroid and kidney epithelial cells. This association provides a mechanism for rapidly reorganizing the membrane cytoskeleton in these cell types through the phosphorylation of ankyrin.

title: Fluorescent probing of urea-induced chemical unfolding of bovine serum albumin by intramolecular charge transfer fluorescence probe E-3-(4-dimethylamino-naphthalen-1-yl)-acrylic acid.
abstract: Changes in polarity at the immediate binding site in protein bovine serum albumin (BSA) produces distinct changes in the solvent polarity-dependent emission band of fluorescence probe E-3-(4-dimethylamino-naphthalen-1-yl)-acrylic acid. Steady-state spectroscopy and time-resolved spectroscopy have been used to investigate this binding process. Attaching the probe to BSA and then monitoring its spectral changes with increasing urea concentration and raising temperature has also tracked the denaturation of BSA chemically and thermally. The polarity of the microenvironment was investigated employing the Reichardt E(T)(30) scale. Fluorescence anisotropy, red edge excitation shifts and acrylamide-induced quenching of fluorescence have been exploited to gain better insight into this binding process.

title: Elimination of Mercury and Organomercurials by Nitrogen-Fixing Bacteria
abstract: Bacteria isolated from mercury-polluted environments are often resistant to mercuric ions (Hg{sup 2+}) and organomercurials. Plasmids determining mercury resistance have been well characterized in gram-negative system. However, in Staphylococcus aureus mercury resistance has been found to be chromosomally determined. The known mechanism of bacterial Hg{sup 2+}-resistance is detoxification of the toxic Hg{sup 2+} by its enzymatic transformation by mercuric reductase to Hg (o). Organomercurial lyase mediates the degradation of organomercurial compounds to Hg{sup 2+}. Mercury and organomercurial resistances have been studied in different bacterial genera. There is little information on Hg-resistance in N{sub 2}-fixing soil bacteria, however, in many developing countries, including India, mercury pollution is still a problem because Hg-based pesticides and fungicides are still used routinely as seed-dressers in agriculture to control soil-borne and seed-borne fungal diseases. Volatilization of Hg from laboratory media by mercury-resistant bacteria containing low levels of mercury has been reported by several workers. It is interesting to note that N{sub 2}-fixing, Hg-resistant soil isolates could volatilize Hg from medium containing very high amounts of HgCl{sub 2}. In the present paper we report the volatilization patterns of five N{sub 2}-fixing bacterial strains, the effect of different inducers on mercuric reductase, and the pattern of substratemore » utilization by organomercurial lyase. In the presence of a low concentration of HgCl{sub 2}. enzymatic detoxification is sufficient to combat the adverse situation created by the presence of Hg{sup 2+} ions. In the presence of a high concentration of HgCl{sub 2}, intracellular sequestration by Hg{sup 2+} binding components may play an additional role in counteracting Hg-toxicity.« less