Photocleavage of myosin subfragment 1 by vanadate

The heavy chain of myosin's subfragment 1 (S1) was cleaved at two distinct sites (termed V1 and V2) after irradiation with UV light in the presence of millimolar concentrations of vanadate and in the absence of nucleotides or divalent metals. The V1 site cleavage appeared to be identical with the previously described active site cleavage at serine-180, which is effected by irradiation of a photomodified form of the S1-MgADP-Vi complex [Cremo, C. R., Grammer, J. C., & Yount, R. G. (1989) J. Biol. Chem. 264, 6608-6011]. The V2 site was cleaved specifically, without cleavage at the V1 site, first by formation of the light-stable S1-Co2+ADP-Vi complex at the active site [Grammer, J. C., Cremo, C. R., & Yount, R. G. (1988) Biochemistry 27, 8408-8415] and then by irradiation in the presence of millimolar vanadate. By gel electrophoresis, the V2 site was localized to a region about 20 kDa from the COOH terminus of the S1 heavy chain. From the results of tryptic digestion experiments, the COOH-terminal V2 cleavage peptide appeared to contain lysine-636 in the linker region between the 50- and 20-kDa tryptic peptides of the heavy chain. This site appeared to be the same site cleaved by irradiation of S1 (not complexed with Co2+ADP-Vi) in the presence of millimolar vanadate as previously described [Mocz, G. (1989) Eur. J. Biochem. 179, 373-378]. Cleavage at the V2 site was inhibited by Co2+ but was not significantly affected by the presence of nucleotides or Mg2+ ions. Tris buffer significantly inhibited V2 cleavage. From the results of UV-visible absorption, 51V NMR, and frozen-solution EPR spectral experiments, it was concluded that irradiation with UV light reduced vanadate +5 to the +4 oxidation state, which was then protected from rapid reoxidation by O2 by complexation with the Tris buffer. The relatively stable reduced form or forms of vanadium were not competent to cleave S1 at either the V1 or the V2 site. 51V NMR titration experiments indicated that a tetrameric species of vanadium preferentially bound to S1 and to the S1-MgADP-Vi complex, whereas no binding of either the monomeric or dimeric species could be detected. These results suggest that the vanadate tetramer was responsible for the photocleavage of S1 which occurred at both the V1 and V2 sites in the absence of nucleotides or divalent metals.     

Etude comparee des proprietes physico-chimiques des mannanes de neuf levures

In order to correlate and compare the antigenic relationships observed between nine yeast strains, we have studied their major antigenic determinant represented by the mannans. This material is a constituent of their cell.The compounds that we have isolated are, in reality, glycopeptides. All their polysaccharide fractions consist of mannose only — except for those of the compounds that we have isolated of R. glutinis and C. lipolytica. All these polysaccharides have very close ramified structures; the only one that seems to be very different is that of R. glutinis, and this is in agreement with the antigenic properties of that yeast.The peptidic fractions of these glycopeptides are rich in threonine, serine and aspartic acid and it is very likely that these amino acids make the link with the polysaccharide fraction. The quantity of these amino acids seem to be affected by the conditions of culture of the yeasts, but not their presence or absence.     

The genetics of cell-mediated lympholysis.

The role of HLA antigens in the generation of cytotoxic cells in CML has been investigated. Cytotoxic effector cells were generated in MLC among HLA-A or HLA-A and HLA-B disparate, HLA-D identical siblings, and among HLA-A and HLA-B disparate, MLC identical (%RR less than or equal to 2 3.6) unrelated individual. The data indicate that HLA-D differences and poliferative MLC responses as measured by 3H-thymidine incorporation are not requisite for the in vitro generation of cytotoxic cells and suggest the existence of a CML-S locus (loci) distinct from HLA-A, HLA-B and HLA-D. The degree of cytotoxicity generated in a proliferative versus a "nonproliferative" MLC was comparable. In addition, these studies demonstrate that antigens other than the currently definable HLA-A, HLA-B, HLA-C, and HLA-D can serve as target determinants in cell-mediated lympholysis.     

Levans. II. Light-scattering and sedimentation data of Streptococcus salivarius Levan in water.

The molecular weights and radii of gyration of Streptococcus salivarius levan fractions were obtained from light-scattering measurements in water. Sedimentation coefficients and partial specific volumes of the fractions were also obtained. Double logarithmic plots of [η] versus M?_w and S⁰ versus M?_w yielded slopes having values of 0.17 and 0.62, respectively. The data and various calculated parameters show that levan from Streptococcus salivarius is highly branched and behaves hydrodynamically as a compact particle of spherical symmetry.     

植被格局对砒砂岩坡地降雨侵蚀的影响

为进一步研究砒砂岩区不同雨型下植被格局对坡面土壤侵蚀特征的影响,基于野外径流小区原位观测试验与景观生态学相结合的方法,通过对比分析不同坡面的植被斑块格局指数与产流产沙之间的相关关系,阐明植被格局对砒砂岩坡地降雨侵蚀的影响。结果表明:(1)该地区降雨可划分为3类,根据各植被坡面产流产沙能力,得出降雨侵蚀力表现为:雨型II(长历时、大雨量、大雨强) ＞ 雨型III(短历时、小雨量、中雨强) ＞ 雨型I(中历时、中雨量、小雨强)。降雨量和最大30min雨强与产流产沙量呈显著或极显著关系,相关系数0.695以上,是预测该区域水土流失的主要降雨因子。(2)各坡面水土保持能力与降雨类型有关,不同雨型下3种植被坡面减流减沙率分别达0.42%、20.8%以上,不同植被格局坡面减沙效益优于减流效益,3种植被坡面的减流能力为:雨型I ＞ 雨型III ＞ 雨型II。(3)3种植被坡面的径流泥沙模数由小到大依次为:均匀分布 ＜ 聚集分布 ＜ 随机分布,对比区域多年平均径流泥沙模数,3种植被坡面能够减少侵蚀达21.33%以上。(4)景观形状指数和分离度指数是影响坡面产流产沙的主要格局因子,相关系数分别达0.884和0.825以上。产流、产沙量与坡面植被斑块分离度呈显著正相关,与景观形状指数呈显著负相关。坡面产流量(Y₁)与斑块分离度(SPLIT)和景观形状指数(LSI)的关系式为Y₁=8.247SPLIT-6.605LSI+38.928,R²=0.905。以上结果表明植被斑块间的分离度越小,形状越复杂,坡面阻力增大,抗侵蚀能力越强。研究成果可为生态恢复过程中植被斑块格局的优化提供理论依据和数据支撑。     

Control of chicken coccidiosis

Coccidiosis could potentially cause enormous economic loss to the poultry industry, especially in the production of broiler chickens (see Box 1). Losses are currently minimized by chemotherapeutic treatment but the effectiveness of many drugs seems to be declining. In this article, Peter Long and Tom Jeffers discuss the future for coccidial chemotherapy, and the potential for immunological control methods.     

刺五加皂苷合成关键酶基因表达的半定量RT-PCR分析

根据已克隆的刺五加鲨烯合酶(squalene synthase,SS)、鲨烯环氧酶(squalene epoxidase,SE)和β-香树酯醇合成酶(β-amyrin synthase,bAS)基因序列信息设计引物,通过半定量RT-PCR分析了SS、SE和bAS基因在刺五加不同生长发育时期和不同器官中表达量的变化.结果表明,SS、SE和bAS基因在各生长发育时期和各器官中均有表达,但表达量差异显著(P<0.05),三者均在盛花期表达量最高,之后降低,进入果实成熟期后SS和bAS的表达量迅速回升,SE无显著变化.SS和bAS在叶片和根中的表达量较高,SE表达量的最大值出现在叶片和幼茎中.刺五加SS、SE和bAS基因的表达间存在显著的正相关关系(P<0.05).研究结果为进一步分析关键酶基因对刺五加三萜皂苷生物合成的影响奠定了基础.