The role of context on alpha-helix stabilization: host-guest analysis in a mixed background peptide model.

The helix content of a series of peptides containing single substitutions of the 20 natural amino acids in a new designed host sequence, succinyl-YSEEEEKAKKAXAEEAEKKKK-NH2, has been determined using CD spectroscopy. This host is related to one previously studied, in which triple amino acid substitutions were introduced into a background of Glu-Lys blocks completely lacking alanine. The resulting free energies show that only Ala and Glu- prove to be helix stabilizing, while all other side chains are neutral or destabilizing. This agrees with results from studies of alanine-rich peptide modela, but not the previous Glu-Lys block oligomers in which Leu and Met also stabilize helix. The helix propensity scale derived from the previous block oligomers correlated well with the frequencies of occurrence of different side chains in helical sequences of proteins, whereas the values from the present series do not. The role of context in determining scales of helix propensity values is discussed, and the ability of algorithms designed to predict helix structure from sequence is compared.     

Polyamine derivatives as inhibitors of trypanothione reductase and assessment of their trypanocidal activities

Trypanothione reductase (TR) occurs exclusively in trypanosomes and leishmania, which are the etiological agents of many diseases. TR plays a vital role in the antioxidant defenses of these parasites and inhibitors of TR have potential as antitrypanosomal agents. We describe the syntheses of several spermine and spermidine derivatives and the inhibiting effects of these compounds on T. cruzi TR. All of the inhibiting compounds displayed competitive inhibition of TR-mediated reduction of trypanothione disulfide. The three most effective compounds studied were N⁴,N⁸-bis(3-phenylpropyl)spermine (12), N⁴,N⁸-bis(2-naphthylmethyl)spermine (14), and N¹,N⁸-bis(2-naphthylmethyl)spermidine (21), with K_i values of 3.5, 5.5 and 9.5 μM, respectively. Compounds 12, 14, and 21 were found to be potent trypanocides in vitro with IC₅₀ values ranging from 0.19 to 0.83 μM against four T. brucei ssp. strains. However, these compounds did not prolong the lives of mice infected with trypanosomes. This work indicates that certain polyamine derivatives which target a unique pathway in Trypanosomatidae have potential as antitrypanosomal agents.     

Physiologic regulation of mixtalol in rape senescence and its yield effects

Physiologic and yield effects of mixtalol at various concentrations sprayed on rape at the anthesis stage were examined. Foliar sprays of 4 and 2 ppm mixtalol significantly increased the chlorophyll content of rape leaves and pods, reduced the accumulation of malondialdehyde and ethylene production, and delayed the degradation of superoxide dismutase and catalase activities of the rape plant. Mixtalol also increased root oxidizability. Meanwhile, the number of branches and pods per plant was increased, and a 10.7% and 8.2% increase of seed yield over the controls was observed with treatments of 4 and 2 ppm mixtalol, respectively. No significant effects from mixtalol were observed on the maturation of plants or on the seed oil content or the erucic acid and glucosinolate content. Total rape oil production increased with 4 and 2 ppm mixtalol significantly by 12.4% and 10.5%, respectively, over the controls.Abbreviations MTL mixtalol - MDA malondialdehyde - TBA thiobarbituric acid - SOD Superoxide dismutase - CAT catalase - TTC tetrazolium     

In vitro culture of Doritaenopsis: comparison between formation of the hyperhydric protocorm-like-body (PLB) and the normal PLB

Characteristics of the hyperhydric protocormlike-bodies (hPLBs) and the normal PLBs (nPLBs) of Doritaenopsis are morphologically and ontogenetically compared. The hPLBs have a translucent and turgid appearance which is due to a lack of air volume in the intercellular spaces. The hPLBs have a lower capacity of shoot formation but a higher capacity of differentiation of new PLBs than the nPLBs. The new PLBs derived from the hPLBs can be recovered from hyperhydricity using a medium containing potato juice. This suggests the possibility that hPLBs can be used for the in vitro propagation of orchid plants.Abbreviations PLB Protocorm-Like-Body - mVW Modified Vacin and Went Medium     

Effect of temperature on the growth,total lipid content and fatty acid composition of recently isolated tropical microalgae Isochrysis sp., Nitzschia closterium,Nitzschia paleacea,and commercial species Isochrysis sp. (clone T.ISO)

The effect of temperature from 10 °C to 35 °C on the growth, total lipid content, and fatty acid composition of three species of tropical marine microalgae, Isochrysis sp., Nitzschia closterium, N. paleacea (formerly frustulum), and the Tahitian Isochrysis sp. (T.ISO), was investigated.Cultures of N. closterium, Isochrysis sp. and T.ISO grew very slowly at 35 °C, while N. closterium did not grow at temperatures higher than 30 °C or lower than 20 °C. N. paleacea was low-temperature tolerant, with cells growing slowly at 10 °C. N. paleacea produced the highest percentage of lipids at 10 °C, while the other species produced maximum amounts of lipid at 20 °C. None of the species maintained high levels of polyunsaturated fatty acids (PUFAs) at high growth temperature and there was a significant inverse relationship between the percentage of PUFAs and temperature for N. paleacea. A curved relationship was found between temperature and percentage of PUFA for N. closterium and tropical Isochrysis sp., with the maximum production of PUFA at 25 °C and 20 °C, respectively. The two Nitzschia species produced higher levels of the essential fatty acid eicosapentaenoic acid [20:5(n-3)] at lower growth temperatures, but the two Isochrysis species had little change in percentage of 20:5(n-3) with temperature. Only T.ISO had the highest percentage of 22:6(n-3) at lowest growth temperature (11.4% total fatty acids at 10 °C).School of Mathematical and Physical SciencesAuthor for correspondence     

Binding characterization of the iron transport receptor from the outer membrane of Escherichia coli (FepA): differentiation between FepA and FecA

The dissociation constants for the binding of ferric enterobactin with FepA and FecA are quantitated with displacement experiments. It is found that K _d for FepA is 12 times lower than the one for FecA. This indicates that FepA is an high-affinity receptor while FecA binds ferric enterobactin with a lower affinity. Monoclonal antibodies specific for binding epitopes of FepA inhibit the binding of ferric enterobactin with purified FepA. These same antibodies do not inhibit the binding of ferric enterobactin with purified FecA. This indicates that the binding epitopes in FecA and FepA are different.     

高压静电场对绵羊精子存活率的影响

采用不同剂量的高压静电场处理绵羊精液,经分析发现,高压静电场对绵羊精具有激活作用。能提高绵羊精液品质,表现在适当剂量的高压静电场能显著地提高绵羊精子存活率,其中以６００ｋＶ／ｍ剂量处理效果最佳。１００ｋＶ／ｍ和３００ｋＶ／ｍ剂量对精子刺激不足,而９００ｋＶ／ｍ剂量则对精子刺激过程,导致部分精子损伤和死亡,同样达不到预期的效果。     

损毁和刺激垂体对大鼠痛阈的影响

采用局限性损毁和刺激垂体的方法,以行为测痛为指标,观察大鼠垂体在痛觉调节中的作用以及地塞米松（Ｄｅｘ）对其影响。实验结果显示,损毁垂体中间叶（ＩＬ）及邻近的前叶（ＡＬ）,大鼠痛阈明显低于手术前的痛阈（Ｐ＜０．０１）。电刺激垂体的上述同样部位,大鼠痛阈明显高于手术基础值及自身假刺激值（Ｐ＜０．００１）。经Ｄｅｘ处理的动物,电刺激垂体不再引起痛阈升高。结果表明,大鼠垂体ＩＬ及靠近ＡＬ与痛调节有关,这种