Effect of spatial dispersion of the dielectric on the binding energy of D- ion in Si and Ge

Using a multivalley effective mass theory, we obtain the binding energy of a D- ion in Si and Ge taking into account the spatial variation of the host dielectric function. We find that on comparison with experimental results the effect of spatial dispersion is important in the estimation of binding energy for the D- formed by As in Si and Ge. The effect is less significant for the case of D- formed by P and Sb donors.

Expression of the extracellular domain of the human heat-stable enterotoxin receptor in Escherichia coli and generation of neutralizing antibodies

The entire extracellular domain of the human heat-stable enterotoxin (ST) receptor as well as a truncated N-terminal domain were cloned as glutathione S-transferase fusion proteins and expressed in Escherichia coli. The recombinant fusion proteins were purified from both the cytosol and the inclusion body fractions by selective detergent extraction followed by glutathione-agarose affinity chromatography. The purified protein, corresponding to the entire extracellular domain, bound the stable toxin peptide with an affinity comparable to that of the native receptor characterized from the human colonic T84 cell line. No binding was observed with the N-terminal truncated fragment of the receptor under similar conditions, Polyclonal antibodies were raised to the entire extracellular domain fusion protein as well as the truncated extracellular domain fusion protein, and the antibodies were purified by affinity chromatography. Addition of the purified antibodies to T84 cells inhibited ST binding and abolished ST-mediated cGMP production, indicating that critical epitopes involved in ligand interaction are present in the N-terminal fragment of the receptor, Purified antibodies recognized a single protein of M(r) 160,000 Da on Western blotting with T84 membranes, corresponding to a size of the native glycosylated receptor in T84 cells. These studies are the first report of the expression, purification, and characterization of any member of the guanylyl cyclase family of receptors in E. coli and show that binding of the toxin to the extracellular domain of the receptor is possible in the absence of any posttranslational modifications such as glycosylation. The recombinant fusion proteins as well as the antibodies that we have generated could serve as useful tools in the identification of critical residues of the extracellular domain involved in ligand interaction.

Analytical approximation solutions for 3-D optical waveguides: Review

The rectangular dielectric waveguide is the most commonly used structure in integrated optics, especially in semi-conductor diode lasers. Demands for new applications such as high-speed data backplanes in integrated electronics, waveguide filters, optical multiplexers and optical switches are driving technology toward better materials and processing techniques for planar waveguide structures. The infinite slab and circular waveguides that we know are not practical for use on a substrate because the slab waveguide has no lateral confinement and the circular fiber is not compatible with the planar processing technology being used to make planar structures. The rectangular waveguide is the natural structure. In this review, we have discussed several analytical methods for analyzing the mode structure of rectangular structures, beginning with a wave analysis based on the pioneering work of Marcatili. We study three basic techniques with examples to compare their performance levels. These are the analytical approach developed by Marcatili, the perturbation techniques, which improve on the analytical solutions and the effective index method with examples.

Orchestration of Haemophilus influenzae RecJ Exonuclease by Interaction with Single-Stranded DNA-Binding Protein

RecJ exonuclease plays crucial roles in several DNA repair and recombination pathways, and its ubiquity in bacterial species points to its ancient origin and vital cellular function. RecJ exonuclease from Haemophilus influenzae is a 575-amino-acid protein that harbors the characteristic motifs conserved among RecJ homologs. The purified protein exhibits a process 5'-3' single-stranded-DNA-specific exonuclease activity. The exonuclease activity of H. influenzae RecJ (HiRecJ) was supported by Mg2+ or Mn2+ and inhibited by Cd2+ suggesting a different mode of metal binding in HiRecJ as compared to Escherichia coli RecJ (EcoRecJ). Site-directed mutagenesis of highly conserved residues in HiRecJ abolished enzymatic activity. Interestingly, substitution of alanine for aspartate 77 resulted in a catalytically inactive enzyme that bound to DNA with a significantly higher affinity as compared to the wild-type enzyme. Noticeably, steady-state kinetic studies showed that H. influenzae single-stranded DNA-binding protein (HiSSB) increased the affinity of HiRecJ for single-stranded DNA and stimulated its exonuclease activity. HiSSB, whose C-terminal tail had been deleted, failed to enhance RecJ exonuclease activity. More importantly, HiRecJ was found to directly associate with its cognate single-stranded DNA-binding protein (SSB), as demonstrated by various in vitro assays, Interaction studies carried out with the truncated variants of HiRecJ and HiSSB revealed that the two proteins interact via the C-terminus of SSB protein and the core-catalytic domain of RecJ. Taken together, these results emphasize direct interactio between RecJ and SSB, which confers functional cooperativity to these two proteins. In addition, these results implicate SSB as being involved in the recruitment of RecJ to DNA and provide insights into the interplay between these proteins in repair and recombination pathways.

The first observation of a Na2TiS2 related structure in a 2-D anionic manganese trimesate intercalated by cationic imidazole

A hydrothermal reaction of Mn(OAc)2·4H2O, trimesic acid, imidazole, KOH and water at 75 °C for 24 h gave rise to a 2-D compound, [HImd][Mn(BTC)(H2O)] (Imd = imidazole; BTC = trimesate), with protonated imidazole molecules occupying the inter-lamellar space, and the structure resembles the classic inorganic compound, the sodium intercalated TiS2 (Na2TiS2).

Interaction of Co, Mn, Mg and AI with d(GCGTACGC): a spectroscopic study

Spectroscopic study on the interactions of trace elements Co, Mn, Mg and Al with d(GCGTACGC) indicated the following: Al and Mg did not alter T-m values. Mn enhanced T-m at lower concentration and decreased it at higher concentrations. Interestingly Co at higher concentration elevated the T-m. These studies also showed lower concentrations of Mn displaced EtBr, whereas Al could displace it at higher ionic strength. Mg and Co displaced EtBr fluorescence at moderate concentrations. The binding constant values and CD spectra clearly indicated strong binding of these elements to DNA.

Early life stress, nicotinic acetylcholine receptors and alcohol use disorders

Stress is a major driving force in alcohol use disorders (AUDs). It influences how much one consumes, craving intensity and whether an abstinent individual will return to harmful alcohol consumption. We are most vulnerable to the effects of stress during early development, and exposure to multiple traumatic early life events dramatically increases the risk for AUDs. However, not everyone exposed to early life stress will develop an AUD. The mechanisms determining whether an individual’s brain adapts and becomes resilient to the effects of stress or succumbs and is unable to cope with stress remain elusive. Emerging evidence suggests that neuroplastic changes in the nucleus accumbens (NAc) following early life stress underlie the development of AUDs. This review discusses the impact of early life stress on NAc structure and function, how these changes affect cholinergic signaling within the mesolimbic reward pathway and the role nicotinic acetylcholine receptors (nAChRs) play in this process. Understanding the neural pathways and mechanism determining stress resilience or susceptibility will improve our ability to identify individuals susceptible to developing AUDs, formulate cognitive interventions to prevent AUDs in susceptible individuals and to elucidate and enhance potential therapeutic targets, such as the nAChRs, for those struggling to overcome an AUD.

Structure of the Monosodium Salt of D-Glucose 6-Hydrogenphosphate

Na+.C6HI209 P-, Mr=282.1, monoclinic, e2~, a=5-762(1), b=7.163(2), c=12.313(1)A, fl= 99.97 (1) °, U= 500.5 A 3, Z= 2, D m = 1.86, D x = 1.87 Mg m -s, Cu Ka, 2 = 1.5418 A, /a = 3-3 mm -1, F(000) = 292, T= 300 K, final R for 922 observed reflections is 0-042. The phosphate ester bond, P-O(6), is 1.575 (5)A, slightly shorter than the P~O bond in monopotassium phosphoenolpyruvate [1.612 (6) A] [Hosur & Viswamitra (1981). Acta Cryst. B37, 839-843]. The pyranose sugar ring takes a 4C 1 chair conformation. The conformation about the exocyclic C(5)-C(6) bond is gauche-trans. The endocyclic C-O bonds in the glucose ring are nearly equal with C(5)-O(5) = 1.435 (8) and C(1)-O(5) = 1.436 (9) A. The sodium ion has seven near neighbours within a distance of 2.9 A. The crystal structure is stabilized by hydrogen bonds between the O atoms of symmetryrelated molecules.

Crystalline A-DNA: The X-Ray Analysis of the Fragment d(G-G-T-A-T-A-C-C)

An A-DNA type double helical conformation was observed in the single crystal X-ray structure of the octamer d(G-G-T-A-T-A-C-C), 1, and its 5-bromouracil-containing analogue, 2. The structure of the isomorphous crystals (space group P61) was solved by a search technique based on packing criteria and R-factor calculations, with use of only low order data. At the present stage of refinement the R factors are 31 % for 1 and 28 % for 2 at a resolution of 2.25 A (0.225 nm). The molecules interact through their minor grooves by hydrogen bonding and base to sugar van der Waals contacts. The stable A conformation observed in the crystal may have some structural relevance to promoter regions where the T-A-T-A sequence is frequently found.

Cholinergic Muscarinic Receptors in Human Fetal Brain: Ontogeny of [3H]Quinuclidinyl Benzilate Binding Sites in Corpus Striatum, Brainstem, and Cerebellum

The ontogeny of muscarinic receptors was studied in human fetal striatum, brainstem, and cerebellum to investigate general principles of synaptogenesis as well as the physiological balance between various chemical synapses during development in a given region of the brain. [3H]Quinuclidinyl benzilate ([-'H]QNB) binding was assayed in total particulate fraction (TPF) from various parts of brain. In the corpus striatum, QNB binding sites are present at 16 weeks of gestation (average concentration 180 fmol/mg protein of TPF), slowly increase up to 24 weeks (average concentration 217 fmol/mg protein), and rapidly increase during the third trimester to 480 fmol/mg protein of TPF. In contrast, dopaminergic receptors exist as two subpopulations. one with low affinity and the other with high affinity up to the 24th week of gestation; all of them acquire the highaffinity characteristic during the third trimester. In brainstem, the muscarinic receptors show maximum concentration by 16 weeks of age (360 fmolimg protein of TPF). Subsequently the muscarinic receptor concentration shows a gradual decline in the brainstem. In cerebellum, except for a slight increase at 24 weeks (average concentration 90 fmol/mg protein of TPF), the receptor concentration remained nearly constant at about 60-70 fmolimg protein of TPF throughout fetal life. This study demonstrates that the ontogeny of muscarinic receptors varies among the different regions, and the patterns observed suggest that receptor formation occurs principally in the third trimester. Also noteworthy is the finding that the QNB binding sites decreased in all regions of the human brain during adult life. Key Words: Cholinergic muscarinic receptors-Quinuclidinyl benzilate-Corpus striaturn-Brainstem-Cerebellum. Ravikumar B. V. and Sastry P. S. Cholinergic muscarinic receptors in human fetal brain: Ontogeny of [3H]quinuclidinyl benzilate binding sites in corpus striatum, brainstem, and cerebellum. J. Neurochem. 45, 1948- 1950 (1985).

Effect of diethylstilbesterol and prolactin on the induction of follicle stimulating hormone receptors in immature and cycling rats

Induction of follicle stimulating hormone receptor in the granulosa cells of intact immature rat ovary by diethylstilbesterol, an estrogen, has been studied. A single injection of 4 mg of diethylstilbesterol produced 72 h later a 3-fold increase in follicle stimulating hormone receptor concentration as monitored by [125I]-oFSH binding to isolated cells. The newly induced receptors were kinetically indistinguishable from the preexisting ones, as determined by Lineweaver-Burk plot of the binding data. The induced receptors were functional as evidenced by increased ability of the granulosa cells to incorporate [3H]-leucine into cellular proteins. Neutralization of endogenous follicle stimulating hormone and luteinizing hormone by administering specific antisera had no effect on the ability of diethylstilbesterol to induce follicle stimulating hormone receptors, whereas blockade of endogenous prolactin secretion by ergobromocryptin administration significantly inhibited (∼ 30 %) the response to diethylstilbesterol; this inhibition could be completely relieved by ovine prolactin treatment. However, ovine prolactin at the dose tried did not by itself enhance follicle stimulating hormone receptor level. Administration of ergobromocryptin to adult cycling rats at noon of proestrus brought about as measured on diestrusII, (a) a reduction of both follicle stimulating hormone (∼ 30 %) and luteinizing hormone (∼ 45 %) receptor concentration in granulosa cells, (b) a drastic reduction in the ovarian tissue estradiol with no change in tissue progesterone and (c) reduction in the ability of isolated granulosa cells to convert testosterone to estradiol in response to follicle stimulating hormone. Ergobromocryptin treatment affected only prolactin and not follicle stimulating hormone or luteinizing hormone surges on the proestrus evening. Treatment of rats with ergobromocryptin at proestrus noon followed by an injection of ovine prolactin (1 mg) at 1700 h of the same day completely reversed the ergobromocryptin induced reduction in ovarian tissue estradiol as well as the aromatase activity of the granulosa cells on diestrus II, thus suggesting a role for proestrus prolactin surge in the follicular maturation process.

Upregulation and Functionality of Neuronal Nicotinic Acetylcholine Receptors

Cigarette smoking is, in developed countries, the leading cause of premature death. In tobacco smoke, the main addictive compound is nicotine, which in the brain binds to neuronal nicotinic acetylcholine receptors (neuronal nAChRs). These have been implicated in addiction, but also in several neurological disorders including Alzheimer's and Parkinson's diseases, Tourette's syndrome, attention-deficit hyperactivity disorder (ADHD), schizophrenia, pain, depression, and autosomal-dominant noctural frontal lobe epilepsy; all of which makes nAChRs an intriguing target of study. Chronic treatment with nicotine leads to an increase in the number of nAChRs (upregulation) in the brain and changes their functionality. Changes in the properties of nAChRs are likely to occur in smokers as well, since they are exposed to nicotine for long periods of time. Several nAChR subtypes likely play a role in the formation of nicotine addiction by participating in the release of dopamine in the striatum. The aim of this study was to clarify at cellular level the changes in nAChR characteristics resulting from chronic nicotine treatment. SH-SY5Y cells, endogenously several nAChR-expressing, and SH-EP1-h-alfa7 cells, transfected with the alfa 7 nAChR subunit gene were treated chronically with nicotine. The localisation of alfa 7 and beta2 subunits was studied with confocal and electron microscopy. Functionality of nAChRs was studied with calcium fluorometry. Effects of long-term treatment with opioid compounds on nAChRs were studied by means of ligand binding. Confocal microscopy showed that in SH-SY5Y cells, alfa7 and beta2 subunits formed clusters, unlike the case in SH-EP1-h alfa7 cells, where alfa7 nAChRs were distributed more diffusely. The majority of nAChR subunits localised on endoplasmic reticulum (ER). The isomers of methadone acted as agonists at alfa7 nAChRs. Acute morphine challenge also stimulated nAChRs. Chronic treatment with methadone or morphine led to an increased number of nAChRs. In animal studies, mice received nicotine for 7 weeks. Electron microscopical analysis of the localisation of nAChRs showed in the striatum that alfa7 and beta2 nAChR subunits localised synaptically, extrasynaptically, and intracellularly, with the majority localising extrasynaptically. Chronic nicotine treatment caused an increase in the number of nAChR subunits at all studied locations. These results suggest that the alfa7 nAChR and beta2 subunit-containing nAChRs respond to chronic nicotine treatment differently. This may indicate that the functional balance of various nAChR subtypes in control of the release of dopamine is altered as a result of chronic nicotine treatment. Compounds binding both to opioid and nACh receptors may be of clinical importance.

The Effects of Nicotine on the Regulation of Neuronal Alpha7 Nicotinic Acetylcholine Receptors and Intracellular Signalling Pathways

Nicotine, the addictive compound of tobacco products, exerts its effects in the brain by binding to neuronal acetylcholine nicotinic receptors (nAChRs). The aim of the present study was to increase the knowledge of nicotine s complex effects, the focus being on homomeric alpha7-nAChRs that are widely expressed in the brain. Nicotinic regulation of differential signalling molecules including transcriptional regulators was also studied. We found that the number of alpha7-nAChRs is increased in specific brain regions in mice, in a time-dependent manner after chronic oral nicotine administration. Our results suggest that in addition to alpha4beta2-nAChRs, the other major nAChR subtype expressed in the brain, the number of alpha7-nAChRs is affected by chronic presence of nicotine. We suggest that when studying the long-term effects of nicotine, the duration on administration is of great importance. Next, we observed that nicotine exposure induces accumulation of cAMP in cell cultures expressing nAChRs. Furthermore, nicotine-induced alpha7-nAChR upregulation was potentiated by treatments enhancing cAMP-signalling, suggesting a role for cAMP in the upregulation process. Protein kinase C (PKC) was found essential for the basal regulation of alpha7-nAChR number. The nicotine-evoked alpha7-nAChR upregulation could be further increased by PKC overexpression. Thirdly, the effects of nicotine on dopamine and cAMP regulated phosphoprotein (DARPP-32) were characterised in rat brain. The results show that DARPP-32 is regulated by both acute and long-term nicotine treatment in the striatal subdivisions. The effect of acute nicotine is dose-dependent and the three striatal regions display differential sensitivities to nicotine. Chronic nicotine is also able to regulate DARPP-32 signalling with prominent effect seen in the nucleus accumbens (NAc), suggesting a role for DARPP-32 in the mediation of long-term effects of nicotine. Finally, the regulation of transcription factors Elk-1 and FosB/deltaFosB by nicotine was investigated. We found that Elk-1 is activated by acute nicotine selectively in the NAc core and hippocampal area CA1, whereas acute nicotine does not affect FosB/deltaFosB. Long-term intermittent or continuous nicotine increases the level of total Elk-1 in the same brain regions as acute nicotine. FosB/deltaFosB is also affected by chronic nicotine. Thus, similarly to other drugs of abuse, nicotine regulates transcriptional regulators Elk-1 and FosB/deltaFosB. These results bring further support for a common mechanism underlying the development of addiction. Nicotine s positive effects on learning and memory might involve the transcription factor Elk-1 based on the changes seen in the hippocampus, the key area in cognitive functions.