On the relationship of thermodynamic parameters with the buried surface area in protein-ligand complex formation

Prediction of thermodynamic parameters of protein-protein and antigen-antibody complex formation from high resolution structural parameters has recently received much attention, since an understanding of the contributions of different fundamental processes like hydrophobic interactions, hydrogen bonding, salt bridge formation, solvent reorganization etc. to the overall thermodynamic parameters and their relations with the structural parameters would lead to rational drug design. Using the results of the dissolution of hydrocarbons and other model compounds the changes in heat capacity (C_p), enthalpy (H) and entropy (S) have been empirically correlated with the polar and apolar surface areas buried during the process of protein folding/unfolding and protein-ligand complex formation. In this regard, the polar and apolar surfaces removed from the solvent in a protein-ligand complex have been calculated from the experimentally observed values of changes in heat capacity (C_p) and enthalpy (H) for protein-ligand complexes for which accurate thermodynamic and high resolution structural data are available, and the results have been compared with the x-ray crystallographic observations. Analyses of the available results show poor correlation between the thermodynamic and structural parameters. Probable reasons for this discrepancy are mostly related with the reorganization of water accompanying the reaction which is indeed proven by the analyses of the energetics of the binding of the wheat germ agglutinin to oligosaccharides.     

Chlorpromazine and other psychoactive drug induced alterations of a membrane bound enzyme in rat brain

Psychoactive drugs like chlorpromazine (CPZ), imipramine, lithium and amphetamine in one way or another affect behaviour. The drug responses are presumably mediated by inducing a change in the activity of membrane bound enzymes. CPZ is very potent in inhibiting the alkaline phosphatase activity in rat brain. The combined effect of CPZ with other drugs shows that CPZ and imipramine together inhibit the enzyme activity significantly greater than the individual inhibition either by CPZ or by imipramine alone. Effective inhibition of the alkaline phosphatase activity with a single drug or combined drugs may lead to a change in neuronal permeability through glucocorticoids thereby affecting mood.     

Growth and thiophene accumulation by hairy root cultures of Tagetes patula in media of varying initial pH

Summary Hairy roots of Tagetes patula were grown for 24 days in modified Murashige and Skoog's liquid medium at different initial pH levels of 4.0, 5.0, 5.7, 6.0 and 7.0. Irrespective of the initial pH, after 12 days, the pH of the culture medium was approximately 4.5. However the final pH, after 24 days of growth, did depend weakly on the initial pH of the medium. The biomass yield was lowest at an initial pH of 4.0, possibly due to lower utilization of ammonium at this pH. Similar patterns of thiophene accumulation was observed at all pH levels tested. Maximum thiophene accumulation occurred in root cultures which were 12–16 days old.Abbreviations BBTOH 5-(4-hydroxy-1-butenyl)-2,2-bithienyl - BBTOAc 5-(4-acetoxy-1-butenyl)-2,2-bithienyl - BBT 5-(3-buten-1-ynyl)-2,2-bithienyl - MS Murashige and Skoog's nutrient medium - B5 Gamborg's B5 nutrient salts - HPLC High pressure liquid chromatography     

p-Toluenesulfonyl Chloride Catalysed Facile Synthesis of O-benzyl-l-amino Acids and Their In Vitro Evaluation

International Journal of Peptide Research and Therapeutics - Protection and subsequent deprotection of amino acid functional groups play a key role in regioselective peptide synthesis. For...     

Cell culture and animal models of viral hepatitis. Part I: hepatitis B

Despite the existence of a preventative vaccine, HBV represents a substantial threat to public health, suggesting the need for research to develop new treatments to combat the disease. The authors review the available in vitro and in vivo models, including recently developed transgenic and chimeric mouse models.     

The human dopamine transporter forms a tetramer in the plasma membrane: cross-linking of a cysteine in the fourth transmembrane segment is sensitive to cocaine analogs

Using cysteine cross-linking, we demonstrated previously that the dopamine transporter (DAT) is at least a homodimer, with the extracellular end of transmembrane segment (TM) 6 at a symmetrical dimer interface. We have now explored the possibility that DAT exists as a higher order oligomer in the plasma membrane. Cysteine cross-linking of wild type DAT resulted in bands on SDS-PAGE consistent with dimer, trimer, and tetramer, suggesting that DAT forms a tetramer in the plasma membrane. A cysteine-depleted DAT (CD-DAT) into which only Cys243 or Cys306 was reintroduced was cross-linked to dimer, suggesting that these endogenous cysteines in TM4 and TM6, respectively, were cross-linked at a symmetrical dimer interface. Reintroduction of both Cys243 and Cys306 into CD-DAT led to a pattern of cross-linking indistinguishable from that of wild type, with dimer, trimer, and tetramer bands. This indicated that the TM4 interface and the TM6 interface are distinct and further suggested that DAT may exist in the plasma membrane as a dimer of dimers, with two symmetrical homodimer interfaces. The cocaine analog MFZ 2-12 and other DAT inhibitors, including benztropine and mazindol, protected Cys243 against cross-linking. In contrast, two substrates of DAT, dopamine and tyramine, did not significantly impact cross-linking. We propose that the impairment of cross-linking produced by the inhibitors results from a conformational change at the TM4 interface, further demonstrating that these compounds are not neutral blockers but by themselves have effects on the structure of the transporter.     

17Beta-estradiol decreases hypoxic induction of erythropoietin gene expression

Exposure to chronic hypoxia induces erythropoietin (EPO) production to facilitate oxygen delivery to hypoxic tissues. Previous studies from our laboratory found that ovariectomy (OVX) exacerbates the polycythemic response to hypoxia and treatment with 17beta-estradiol (E2-beta) inhibits this effect. We hypothesized that E2-beta decreases EPO gene expression during hypoxia. Because E2-beta can induce nitric oxide (NO) production and NO can attenuate EPO synthesis, we further hypothesized that E2-beta inhibition of EPO gene expression is mediated by NO. These hypotheses were tested in OVX catheterized rats treated with E2-beta (20 microg/day) or vehicle for 14 days and exposed to 8 or 12 h of hypoxia (12% O(2)) or normoxia. We found that E2-beta treatment significantly decreased EPO synthesis and gene expression during hypoxia. E2-beta treatment did not induce endothelial NO synthase (eNOS) expression in the kidney but potentiated hypoxia-induced increases in plasma nitrates. We conclude that E2-beta decreases hypoxic induction of EPO. However, this effect does not appear to be related to changes in renal eNOS expression.     

Distribution of sibling species of Anopheles culicifacies s.l. and Anopheles fluviatilis s.l. and their vectorial capacity in eight different malaria endemic districts of Orissa, India

The study was undertaken in eight endemic districts of Orissa, India, to find the members of the species complexes of Anopheles culicifacies and Anopheles fluviatilis and their distribution patterns. The study area included six forested districts (Keonjhar, Angul, Dhenkanal, Ganjam, Nayagarh and Khurda) and two non-forested coastal districts (Puri and Jagatsingpur) studied over a period of two years (June 2007-May 2009). An. culicifacies A, B, C and D and An. fluviatilis S and T sibling species were reported. The prevalence of An. culicifacies A ranged from 4.2-8.41%, B from 54.96-76.92%, C from 23.08-33.62% and D from 1.85-5.94% (D was reported for the first time in Orissa, except for occurrences in the Khurda and Nayagarh districts). The anthropophilic indices (AI) were 3.2-4.8%, 0.5-1.7%, 0.7-1.37% and 0.91-1.35% for A, B, C and D, respectively, whereas the sporozoite rates (SR) were 0.49-0.54%, 0%, 0.28-0.37% and 0.41-0.46% for A, B, C and D, respectively. An. fluviatilis showed a similarly varied distribution pattern in which S was predominant (84.3% overall); its AI and SR values ranged from 60.7-90.4% and 1.2-2.32%, respectively. The study observed that the co-existence of potential vector sibling species of An. culicifacies (A, C and D) and An. fluviatilis S (> 50%) was responsible for the high endemicity of malaria in forested districts such as Dhenkanal, Keonjhar, Angul, Ganjam, Nayagarh and Khurda (> 5% slide positivity rate). Thus, the epidemiological scenario for malaria is dependent on the distribution of the vector sibling species and their vectorial capacity.