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.     

重组人粒细胞-巨噬细胞集落刺激因子包涵体提取、复性和纯化的研究

由基因工程大肠杆菌表达的重组人粒细胞－巨噬细胞集落刺激因子（ｒｈＧＭ－ＣＳＦ）以包涵体的形式存在于细胞中,通过破菌、洗涤获得包涵体,再经过溶解、凝胶过滤、复性、疏水和离子交换柱导析得到了均一的产品,经高压液相和ＳＤＳ－ＰＡＧＥ电泳测定纯度均大于９８％,ｒｈＧＭ－ＣＳＦ的比活为３．２×１０＾７ＩＵ／ｍｇ,纯化获得的ｒｈＧＭ－ＣＳＦ为一酸性蛋白,等电点约为５．２,ＮＨ２－末端有２０个氨基酸序列测定结果     

国产前原鹅观草的订正

对我国文献中记载的前原鹅观草（Ｒｏｅｇｎｅｒｉａｍａｙｅｂａｒａｎａ（Ｈｏｎｄａ）Ｏｈｗｉ）的标本和植物,与原产于日本的该种进行了比较形态学、细胞学研究,二者差异显著。作者认为我国所记载的该种种名应是山东鹅观草（Ｒｏｅｇｎｅｒｉａｓｈａｎｄｏｎｇｅｎｓｉｓ（Ｂ．Ｓａｌｏｍｏｎ）Ｊ．Ｌ．Ｙａｎｇ,Ｙ．Ｈ．ＺｈｏｕｅｔＹｅｎ）,其内稃先端钝圆,长为外稃的３／４,染色体数为２ｎ＝４ｘ＝２８,具ＳＹ染色体组,结实率达９０％以上,过去被错定为Ｒ．ｍａｙｅｂａｒａｎａ。而Ｒ．ｍａｙｅｂａｒａｎａ在日本系一天然杂种,其内稃先端尖,与外稃等长或稍短,染色体数为２ｎ＝６ｘ＝４２,具ＨＳＹ染色体组,结实率极低,仅０．２％～０．４％。     

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.     

Role of sialyloligosaccharide binding in Theiler's virus persistence.

Theiler's murine encephalomyelitis viruses (TMEVs) belong to the Picornaviridae family and are divided into two groups, typified by strain GDVII virus and members of the TO (Theiler's original) group. The highly virulent GDVII group causes acute encephalitis in mice, while the TO group is less virulent and causes a chronic demyelinating disease which is associated with viral persistence in mice. This persistent central nervous system infection with demyelination resembles multiple sclerosis (MS) in humans and has thus become an important model for studying MS. It has been shown that some of the determinants associated with viral persistence are located on the capsid proteins of the TO group. Structural comparisons of two persistent strains (BeAn and DA) and a highly virulent strain (GDVII) showed that the most significant structural variations between these two groups of viruses are located on the sites that may influence virus binding to cellular receptors. Most animal viruses attach to specific cellular receptors that, in part, determine host range and tissue tropism. In this study, atomic models of TMEV chimeras were built with the known structures of GDVII, BeAn, and DA viruses. Comparisons among the known GDVII, BeAn, and DA structures as well as the predicted models for the TMEV chimeras suggested that a gap on the capsid surface next to the putative receptor binding site, composed of residues from VP1 and VP2, may be important in determining viral persistence by influencing virus attachment to cellular receptors, such as sialyloligosaccharides. Our results showed that sialyllactose, the first three sugar molecules of common oligosaccharides on the surface of mammalian cells, inhibits virus binding to the host cell and infection with the persistent BeAn virus but not the nonpersistent GDVII and chimera 39 viruses.     

Phosphorylation of rat muscle acetyl-CoA carboxylase by AMP-activated protein kinase and protein kinase A

Winder, W. W., H. A. Wilson, D. G. Hardie, B. B. Rasmussen,C. A. Hutber, G. B. Call, R. D. Clayton, L. M. Conley, S. Yoon, and B. Zhou. Phosphorylation of rat muscle acetyl-CoA carboxylase byAMP-activated protein kinase and protein kinase A. J. Appl. Physiol. 82(1): 219-225, 1997This studywas designed to compare functional effects of phosphorylation of muscleacetyl-CoA carboxylase (ACC) by adenosine 3,5-cyclicmonophosphate-dependent protein kinase (PKA) and by AMP-activatedprotein kinase (AMPK). Muscle ACC (272 kDa) was phosphorylated and thensubjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresisfollowed by autoradiography. Functional effects of phosphorylation weredetermined by measuring ACC activity at different concentrations ofeach of the substrates and of citrate, an activator of the enzyme. Themaximal velocity(V_max) and theMichaelis constants(K_m) for ATP,acetyl-CoA, and bicarbonate were unaffected by phosphorylation by PKA.Phosphorylation by AMPK increased theK_m for ATP andacetyl-CoA. Sequential phosphorylation by PKA and AMPK, first withoutlabel and second with label, appeared to reduce the extent of label incorporation, regardless of the order. The activation constant (K_a) forcitrate activation was increased to the same extent by AMPKphosphorylation, regardless of previous or subsequent phosphorylation by PKA. Thus muscle ACC can be phosphorylated by PKA but with noapparent functional effects on the enzyme. AMPK appears to be the moreimportant regulator of muscle ACC.

     

Characterization of progenies of Triticum aestivum- Psathyrostachys juncea derivatives by using genomic in-situ hybridization

Using genomicin-situ hybridization (GISH) technique, 7 translocation-addition lines, 6 translocation and translocation-addition lines, 2 ditelosomic addition lines and 1 translocation line were identified fromTriticum aestivum L. -Psathyrostachys juncea (Fisch.) Nevski intergeneric hybrids, of which translocation-addition and translocation and translocation-addition lines were not found in other reports. No substitutions and disornic additions were detected in the, hybrids and breakages occurred in allP. juncea chromosomes studied. Results have shown that the improved GISH technique is a rapid and economical method for use in this field.     

脱落酸对线粒体Na^＋—K^＋ATPase活性的影响

在提取大豆（Ｇｌｙｃｉｎｅ ｍ ａｘ）黄化子叶的线粒体时,于清洗和悬浮介质中加入ＡＢＡ,发现４０ μｍ ｏｌ／Ｌ（±） ＡＢＡ 对线粒体膜结合Ｎａ＋ －Ｋ＋ ＡＴＰａｓｅ 活性及线粒体吸氧速率有明显的促进作用。ＡＢＡ 可使１６℃与２７℃培养的大豆子叶线粒体膜结合Ｎａ＋ －Ｋ＋ ＡＴＰａｓｅ Ａｒｒｈｅｎｉｕｓ图的折点温度分别下降６．３℃和５．９℃,并将该酶的底物动力学曲线由正协同曲线转变为非协同曲线。表明ＡＢＡ 可降低线粒体的膜相变温度     

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