Protein dynamics: conformational disorder,vibrational coupling and anharmonicity in deoxy-hemoglobin and myoglobin

In this work we study the temperature dependence of the Soret band lineshape of deoxymyoglobin and deoxyhemoglobin, in the range 300–20 K. To fit the measured spectra we use an approach originally proposed by Champion and coworkers (Srajer et al. 1986; Srajer and Champion 1991). The band profile is modelled as a Voigt function that accounts for the coupling with low frequency vibrational modes, whereas the coupling with high frequency modes is responsible for the vibronic structure of the spectra. Moreover, owing to the position of the iron atom out of the mean heme plane, inhomogeneous broadening brings about a non-Gaussian distribution of 0–0 electronic transition frequencies. The reported analysis enables us to isolate the various contributions to the overall bandwidth, and their temperature dependence points out the relevance of low frequency vibrations and of large scale anharmonic motions starting at temperatures higher than 170 K. Information on the mean iron-heme plane distance and on its temperature dependence, as well as on the heme pocket conformational disorder, is also obtained.Abbreviations Cc Carbon monoxide - Hb Human deoxyhemoglobin A - HbCO human carbonmonoxyhemoglobin A - SWMb spermwhale deoxymyoglobin - SWMbCO spermwhale carbonmonoxymyoglobin - HbO₂ human oxyhemoglobin A - SWMb³⁺-H₂O spermwhale aquometmyoglobin     

Effect of cytokinins on plastid development and photosynthetic polypeptides during organogenesis ofPinus ponderosa Dougl. cotyledons culturedin vitro

InPinus ponderosa Dougl., application of the cytokinins, benzyladenine and 2-isopentenyl adenine, to excised cotyledons, promoted thein vitro formation of meristematic centers which led to bud and shoot production. Meristematic cells showed plastids with poorly developed thylakoid membranes and rudimentary grana, whereas cells in non-meristematic tissues and in growth regulator free medium, had chloroplasts with well developed inner membranes, and more thylakoid membranes and grana than plastids of meristematic cells. Chlorophyll and six polypeptides associated with photosynthesis were present in lower concentrations in cytokinin-treated cotyledons than in those cultured in growth regulator free medium. Both benzyladenine and 2-isopentenyl adenine are effective in inhibiting the accumulation of at least two photosynthetic polypeptides in the first 24 h in culture. The ability of cotyledons to respond in this way to cytokinins is lost after three days in culture in growth regulator free medium prior to treatment with cytokinin.     

Soil-eating byAlouatta andAteles

Among 12 species of New World monkeys studied in La Macarena Region and the River Caquetá basin of Colombia, onlyAlouatta seniculus andAteles belzebuth were frequently observed to eat soil. They do this at particular sites on the ground called salados by local people. They also eat termite nests found on tree trunks. OnlyAteles drink the water of salado sites. The chemical properties of 17 soil samples and 5 water samples were analyzed. The results are discussed in relation to the question of whyAlouatta andAteles eat soil.     

菜心溶菌酶的提纯及酶学性质

菜心（ＢｒａｓｓｉｃａｃａｍｐｅｓｔｒｉｓＬ．ｓｓｐ．ｃｈｉｎｅｎｓｉｓｖａｒ．ｕｔｉｌｉｓ）叶子高速捣碎后,滤液经酸碱处理,硫酸铵分步沉淀,凝胶柱层析等步骤分离纯化溶菌酶,酶比活力达３４１４．６Ｕ／ｍｇ,纯化倍数为１９７．４。菜心溶菌酶在较宽的温度或ｐＨ值范围均有活性,最适温度为６０℃,最适ｐＨ值为５．８,底物Ｋｍ值为８７μｇ／ｍＬ。该酶对热和酸碱的稳定性较高,巯基和酪氨酸残基不是该酶活性中心的必需基团。     

小球藻RubisCO的纯化及其在异养向自养转变过程中的含量变化

经硫酸铵分部沉淀、ＳｅｐｈａｃｒｙｌＳ－３００和ＤＥＡＥ－纤维素柱层析纯化了小球藻ＲｕｂｉｓＣＯ,得率为１５％,比活力达１．２３２μｍｏｌＣＯ２ｍｓ－１ｍｉｎ－１,分子量是５００ｋＤ,它和菠菜叶片ＲｕｂｉｓＣＯ在分子量、亚基组成和免疫特性等方面相似,反映ＲｕｂｉｓＣＯ在高等和低等植物中有较高的同源性。自养小球藻ＲｕｂｉｓＣＯ占细胞可溶性蛋白质的２４％。而异养转变后的小球藻细胞内不含ＲｕｂｉｓＣＯ。异养小球藻向自养生长转变过程中,２０ｈ后细胞内叶绿素含量逐渐增加,２４ｈ时细胞内出现ＲｕｂｉｓＣＯ,２４ｈ后大量增加,至４１ｈ时含量达最高峰;标志着小球藻细胞光合作用能力的恢复和加强。     

Estimation of disruption of animal cells by turbulent capillary flow

Disruption of animal cells in turbulent capillary flows has been predicted from a model of cell-hydrodynamic interactions using cell mechanical properties determined by micromanipulation. Eddies of sizes similar to or smaller than the cells are presumed to interact with those cells, causing local surface deformations. The proposed mechanism of cell damage is that such deformations result in an increase in membrane tension and surface energy and that a cell disrupts when its bursting membrane tension and bursting surface energy are exceeded. The surface energy of the cells is estimated from the kinetic energy of appropriately sized eddies. To test the model, cells were disrupted in turbulent flows in capillaries at mean energy dissipation rates up to 2 x 10(4) m(2)/s(3). In all cases the model underestimated the cell disruption by about 15%. Such good agreement implies that the approach of the model to the complicated phenomena of cell turbulence interactions is reasonable. (c) 1993 John Wiley & Sons, Inc.     

Diatom ecology in the phyllosphere of the common duckweed (Lemna minor L.)

Epiphyton associated with thick, floating mats of the common duckweed (Lemna minor L.) was studied at four sites in western Canada between 1985 and 1988. Maximum epiphyton abundance generally occurred in spring as biomass of the duckweed mat was increasing. Epiphytic biomass was low during summer and increased at some sites in autumn with mat decomposition. The community was composed mostly of diatoms and, during summer, photosynthetic bacteria. Species richness of the diatom flora was low, suggesting that duckweed mats are environments to which few species are adapted. Photosynthesis - irradiance curves indicated that duckweed epiphyton was not adapted to low light levels that occurred in the mat (< 1 % of ambient), suggesting they may survive via other means of nutrition. The mat phyllosphere was also characterized by wide spatial and temporal variation in temperature, and sharp vertical profiles of dissolved oxygen and nutrients.     

Culture of rotifers with reference to some physico-chemical properties of water in nursery pond

Rotifers were cultured with five different organic and inorganic fertilizers in nursery ponds. Of the fertilizers used, mustard oil cake gave significantly (p < 0.01) higher production of rotifers than that of mohua oil cake followed by cow-dung, wheat bran, mixture of NPK and control. The higher production of rotifers was directly related with the higher doses of fertilizers. Among the rotifer species identified, the abundance of Brachionus caudatus and B. forficula were significantly (p < 0.01) higher than others. Available N, available P, exchangeable K and exchangeable Ca and exchangeable Mg were generally higher in ponds where organic fertilizers were used. Proximate composition of rotifers varied depending on the kinds of fertilizers. The multiple correlations of physico-chemical properties were highly significant (p < 0.01) with the growth and production of B. caudatus (R = 0.995), B. forficula (R = 0.932), Trichocerca capucina (R = 0.917), B. patulus (R = 0.901) and B. angularis (R = 0.892) and simply significant (p < 0.05) in the case of Keratella tropica (R = 0.880), Hexarthra intermadia (R = 0.875), B. calyciflorus (R = 0.864) and Filinia spp. (R = 0.856) contributing 91.20%, 86.86%, 84.09%, 81.18%, 79.57%, 77.44%, 76.56%, 74.65% and 73.27% of total effect of water properties on the growth of these species, respectively. The residual effect of nine different physico-chemical properties of water on the production of rotifers was 78.92% which indicates that these properties of water had only 21.08% influence on the production of rotifers.     

Some properties and occurrence of cytochrome c-552 in the aerobic photosynthetic bacterium Roseobacter denitrificans

Characteristics and occurrence of cytochrome c-552 from an aerobic photosynthetic bacterium, Roseobacter denitrificans, were described.Relative molecular mass of the cytrochrome was 13.5 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 15,000 by gel filtration. This cytochrome was a acidic protein having a pI of 5.6 and E_m was +215 mV at pH 7.0. Absorption peaks were at 278, 408 and 524 nm in the oxidized form and 416, 523 and 552 nm in the reduced form.Amino acid composition and N-terminal amino acid sequence of cytochrome c-552 determined for 24 residues had low similarities to those of cytochrome c-551 of this bacterium, which is homologous to cytochrome c ₂, although the physico-chemical properties of these two cytochromes were similar to each other.Cytochrome c-552 was maximally synthesized in the light under aerobic conditions but not in the dark. The synthesis also occurred in the presence of alternative acceptors such as trimethylamine N-oxide (TMAO) and nitrate under anaerobic conditions. Our results suggest that cytochrome c-552 is involved in TMAO respiration and denitrification in R. denitrificans, although the effect of light remains to be solved.Abbreviations E_m Midpoint redox potential - PAGE Polyacrylamide ge electrophoresis - SDS-PAGE Sodium dodecyl sulfate polyacrylamide gel electrophoresis - TMAO Trimethylamine N-oxide     

不同密度格木幼林的土壤理化与林下植被特征

为探索适合格木(Erythrophleum fordii)人工林在幼龄阶段的种植密度,在不同林分密度(2 m×1 m、2 m×2 m、2 m×3 m、3 m×3 m)的6 a生格木人工林下设置标准样地,采用土壤质量评价和灰色关联度等方法,探究不同密度下格木幼林的土壤理化与林下植被特征。结果表明,密度2 m×3 m下的林木胸径、树高最优,较最低水平高16.7%、27.9%;土壤总孔隙度最大,全N、硝态N、铵态N含量最高,灌木草本多样性最高。相关性分析表明土壤化学性质对灌木草本的多样性影响最大。不同林分密度下格木幼林土壤理化性质及林下植物多样性有显著差异,因此,选择合适的林分密度对人工林土壤肥力的可持续利用及林分的经营培育至关重要。