白洋淀土壤中多环芳烃的分布特征及来源

采用气相色谱质谱联用仪检测了白洋淀表层(0～20 cm)和亚表层(20～30或农田30～40 cm)土壤中16种多环芳烃的含量。结果表明：表层土壤中多环芳烃总量的变化范围为146.0～645.9 ng·g^-1,平均含量为417.4 ng·g^-1;亚表层土壤中多环芳烃总量的变化范围为43.0～394.5 ng·g^-1,平均含量为152.4 ng·g^-1。表层土壤中多环芳烃含量与有机碳含量相关性不显著,亚表层土壤中多环芳烃含量与有机碳含量呈显著正相关(P<0.01),这可能表明了土壤埋藏改造过程中PAHs与土壤有机相结合程度不断加强,以及土壤中不同环数多环芳烃的环境行为差异,总体上看,与高环(≥4环)多环芳烃相比,萘、菲等低环(2～3环)多环芳烃更容易向下层迁移。PAHs的源解析分析表明,白洋淀表层土壤的多环芳烃表现出显著的以生物质和煤燃烧为主的源特征,这与淀区的人为活动,如秸秆燃烧等相关。     

沈阳市铁西区老工业搬迁区土壤多环芳烃的健康风险评价

采用美国能源部风险评估信息系统的暴露量化方法和美国环保局健康风险评估手册的风险表征方法,评估了沈阳市铁西区老工业搬迁区土壤中15种多环芳烃对户外劳作者的健康风险.沈阳市铁西区老工业搬迁区土壤中多环芳烃含量为290.9～8492.37μg·kg-1,搬迁区户外劳作者由于土壤中多环芳烃引起的非致癌危害指数范围为6.39×10-6 ～ 3.04×10-4,致癌风险范围为2.08×10-7 ～7.52×10-6,可判定对人体健康的危害较小.沈阳市铁西区老工业搬迁区致癌多环芳烃含量最高暴露点致癌风险值为7.52×10-6,未超过致癌风险水平上限(10-4),致癌风险尚在可接受范围内.多环芳烃中苯并(a)芘对综合致癌风险贡献最大,贡献率高达61.0％,应注意防范土壤中该污染物引起的健康危害.沈阳市铁西区老工业搬迁区户外劳作者受到的非致癌危害和致癌风险主要由经口摄入途径和皮肤接触途径贡献,两种途径对非致癌危害和致癌风险贡献率分别达到99％和100％,呼吸摄入引起的非致癌危害和致癌风险则相对较小.     

糙皮侧耳和鞘脂菌NS7对多环芳烃污染土壤的生物强化与协同作用

[背景] 真菌和细菌被认为在多环芳烃污染土壤生物修复过程中发挥协同作用,目前在真实土壤体系中开展真菌-细菌协同降解研究较少。[目的] 研究真菌和细菌对不同种类多环芳烃降解的差异及对蒽和苯并[a]蒽的生物强化与协同作用。[方法] 选用多环芳烃降解真菌和细菌各一株,在液体纯培养体系下分析它们对不同种类多环芳烃降解的差异,在土壤体系中采用放射性同位素示踪技术研究2种微生物对蒽和苯并[a]蒽的生物强化与协同作用。[结果] 供试细菌鞘脂菌NS7能够很好地降解低环种类多环芳烃,以蒽作为唯一碳源时可以将其完全降解,在复合污染条件下对菲、蒽、荧蒽、芘等降解效果突出（>90%）,对苯并[a]芘降解效果较差（9.76%）。相比而言,供试真菌糙皮侧耳菌对苯并[a]芘具有更好的降解效果（21.18%）,对低环多环芳烃降解效果明显不如降解菌NS7。在自然土壤中,蒽和苯并[a]蒽具有明显不同的矿化效率,分别为18.61%和4.28%,在蒽污染土壤中加入鞘脂菌NS7并未显著提高蒽的矿化率（P>0.05）,相比而言,苯并[a]蒽污染土壤中加入糙皮侧耳显著提高了污染物矿化效率（2.24倍）,表明真菌和细菌在土壤环境中的定殖存活能力可能影响了生物强化效果。采用灭菌土壤排除土著微生物的竞争排斥作用,研究了真菌菌丝对生物强化降解的影响,发现在蒽污染土壤中,真菌菌丝的迁移作用显著提高了细菌鞘脂菌NS7对污染物的矿化率,从1.75%提高到5.91%;而在苯并[a]蒽灭菌污染土壤中,接种糙皮侧耳却没有发现苯并[a]蒽矿化率提高的现象,表明自然土壤中真菌强化降解苯并[a]蒽的作用可能是源于真菌菌丝促进污染物和土著降解菌的接触,而非直接来自真菌本身。[结论] 细菌能够很好地降解低环种类多环芳烃,而真菌对高环种类多环芳烃降解效果较好。真菌可能通过菌丝促进土著微生物在土壤中的迁移,增大多环芳烃和土著降解菌的接触,从而促进了多环芳烃降解。研究加深了对多环芳烃污染土壤生物强化修复的认识,对发展基于真菌-细菌协同作用的生物强化与调控技术提供理论指导。     

温度和水分变化对冻土区泥炭地土壤氮循环功能基因丰度的影响

以大兴安岭多年冻土区泥炭地为研究对象,通过室内模拟增温实验,研究温度升高对不同深度（0-150 cm）土壤氮循环功能基因丰度的影响。同时针对0-20 cm和20-40 cm土壤设置两个水分处理,分别为土壤原始含水量和淹水状态,研究水分变化对表层土壤氮循环功能基因丰度的影响。结果表明温度升高显著提高了活动层（0-60 cm）、过渡层（60-80 cm）、永冻层（80-100 cm）中nifH、nirK基因丰度,温度升高显著提高了活动层（0-40 cm）和过渡层（60-80 cm）中nirS基因丰度。温度升高显著提高了过渡层（60-80 cm）NH₄⁺-N和较深永冻层（140-150 cm）NO₃^--N的含量,但降低了过渡层（60-80 cm）NO₃^--N和较深永冻层（120-150 cm）NH₄⁺-N的含量,相关性分析表明,NH₄⁺-N含量与nifH和nirS基因丰度呈显著正相关,NO₃^--N含量与nirK基因丰度呈显著正相关,说明温度升高能够通过改变微生物丰度促进过渡层固氮作用和反硝化作用。在增温条件下,淹水处理使表层土壤nirS和nirK基因丰度及NH₄⁺-N含量降低,但提高了NO₃^--N含量,说明淹水造成了过度还原的条件使反硝化底物浓度降低,降低反硝化微生物活性进而抑制了土壤反硝化作用。该结果对于明确未来气候变化影响下冻土区泥炭地土壤氮循环过程具有重要意义。     

川中丘陵区冬水田种植模式转旱作土壤呼吸组分特征及碳平衡

冬水田-水稻是川中丘陵区传统的稻田种植模式,冬水田种植模式转变是实现多熟种植及机械化的重要途径。为探究冬水田-水稻种植模式转旱作过程中作物季及休闲期土壤呼吸速率及其组分构成,试验设置冬水田-水稻转旱作(FTD)、冬水田-水稻(FR)和冬闲田-玉米(FM)3种不同种植模式,采用根排除法和静态明箱-气相色谱法原位取样测定作物季及季后休闲期土壤呼吸及其组分,并通过测算净生态系统生产力(NEP)进而判断冬水田-水稻转旱作过程的农田系统碳汇强度。结果表明:(1)FTD显著提高了土壤总呼吸速率及其自养和异养呼吸速率,从而提高了其累积排放量(P<0.05)。与FR相比,FTD的土壤总呼吸及其自养和异养呼吸的累积排放量分别提高了13.14倍、11.32倍和15.56倍(P<0.05);与FM相比,FTD的土壤总呼吸及其自养和异养呼吸的累积排放量分别提高了70.56%、40.83%和115.47%(P<0.05)。(2)与FR和FM相比,FTD均降低了土壤呼吸及其组分的温度敏感性(Q₁₀),且土壤总呼吸的温度敏感性介于异养呼吸和自养呼吸之间。(3)FR,FM和FTD的净生态系统生产力(NEP)均为正值,其数值分别为7911.66 kg/hm²,5667.89 kg/hm²和1583.46 kg/hm²,均表现为大气CO₂的碳汇,但与FR与FM相比,FTD显著降低了其净生态系统生产力,呈现出较弱的碳汇。     

镉吸附细菌的分离及其对土壤镉的固定

[目的] 探究镉吸附细菌是否能够高效固定土壤有效镉（Cd）,为土壤有效Cd的微生物固定提供理论依据。[方法] 利用含Cd²⁺牛肉膏蛋白胨液体培养基对细菌进行Cd的耐受性测试筛选出镉抗性强的菌株;通过16S rRNA基因相似性及系统进化分析鉴定耐镉细菌,将菌细胞加入含CdCl₂溶液中进行Cd²⁺吸附效率测定;通过土培模拟实验,测定土壤pH、碱解氮、有效磷、速效钾、有机质、CEC、有效Cd及微生物数量来分析镉吸附细菌对镉污染土壤的影响。[结果] 从德阳鱼腥草根际土壤中分离获得的57株细菌对Cd²⁺表现出不同程度的抗性,并从中筛选出3株耐Cd优势细菌普罗威登斯菌属（Providencia）DY8、芽孢杆菌属（Bacillus）DY3和芽孢杆菌属（Bacillus）DY1-4。其对溶液中的Cd²⁺表现出较好的吸附作用,吸附效率随着Cd²⁺浓度升高而降低。DY8、DY3、DY1-4能使镉污染土壤中有效Cd含量分别降低72.11%、68.55%、62.32%,同时显著提高镉污染土壤中碱解氮、有效磷的含量。[结论] Cd污染农田土壤中含有丰富的耐Cd微生物资源,Cd吸附细菌能降低土壤中有效Cd的含量,且能有效改善土壤养分条件。     

模拟氮沉降对石栎和苦槠幼苗土壤呼吸的影响

用LI-8100开路式土壤碳通量测量系统测定模拟氮沉降4种不同处理水平(0、60、120\,240 kg · hm^-2 · a^-1)下石栎(Lithocarpus glabra)和苦槠(Castanopsis sclerophylla)幼苗的土壤呼吸速率及土壤温度、含水量对其土壤呼吸的影响。结果表明,氮沉降对土壤呼吸的影响根据施氮水平和幼苗的种类不同而异。低氮(60 kg · hm^-2 · a^-1)处理下石栎和苦槠的土壤呼吸速率平均值分别为(4.014±0.812)μmol · m^-2 · s^-1和(5.170±0.689)μmol · m^-2 · s^-1,比对照组(0 kg · hm^-2 · a^-1)土壤呼吸速率平均值(3.802±0.948)μmol · m^-2 · s^-1和(3.557±0.906)μmol · m^-2 · s^-1分别高5%和45%;两树种在中、高氮处理下均出现对土壤呼吸明显的抑制。其中石栎中、高氮实验组的土壤呼吸速率分别为(2.653±0.681)μmol · m^-2 · s^-1、(2.592±0.736)μmol · m^-2 · s^-1, 比对照组低27%和29%。苦槠中、高氮实验组的土壤呼吸速率为(3.563±0.402)μmol · m^-2 · s^-1、(3.466±0.994)μmol · m^-2 · s^-1, 比对照组低7%和8%;石栎在高氮(240 kg · hm^-2 · a^-1)处理水平下,其土壤呼吸速率同10cm土壤温度之间呈现显著的指数关系(R²=0.811,P=0.001),而在低、中氮实验均未发现有明显指数关系。苦槠各处理水平下其土壤呼吸与土壤温度之间均未发现有明显的指数关系;在土壤呼吸与5cm土壤含水量的相关性方面,仅有苦槠高氮实验组表现出明显的二次方程关系(R²=0.722),而其低、中氮实验组及石栎各实验组均未有明显的相关性;与单因素(温度、含水量)拟合它们与土壤呼吸速率的方程相比,多元回归分析得到的土壤呼吸速率同土壤温度和含水量之间的拟合方程在P=0.05水平上能更好地解释土壤呼吸的变化情况。石栎和苦槠在氮沉降处理下的土壤呼吸温度系数Q₁₀值分别为2.29、1.95、1.59和1.46、1.41、1.76,同对照组2.64和1.78相比,均有明显降低,且两者Q₁₀值的变化分别呈递减和先减小后增大的趋势,表明氮沉降是影响石栎和苦槠土壤CO₂通量的一个重要因素。     

不同氮素添加量对大兴安岭冻土区泥炭地植物细根形态的影响模拟研究

为探讨氮素营养环境变化对冻土区泥炭地植物细根形态的影响,在大兴安岭泥炭地开展了不同浓度氮素添加模拟试验,添加量分别为0 g N m^-2 a^-1（CK）、6 g N m^-2 a^-1（N1）、12 g N m^-2 a^-1（N2）和24 g N m^-2 a^-1（N3）。在2020年8月和9月,利用微根管技术观测泥炭地不同深度（0-20 cm、20-40 cm）土壤中的植物细根形态,应用WinRHIZO图像分析软件分析根系特征。结果表明,在表层土壤（0-20 cm）中植物细根的总根长、总表面积、总体积和根长密度随施氮量增加而增加,其中8月份N3处理下细根总根长、总表面积、总体积和根长密度显著高于其他处理（P< 0.05）,N2处理下细根总表面积、总体积显著高于对照组和N1处理;9月份N3处理下细根总根长和根长密度显著高于对照组,总表面积和总体积显著高于对照组和N1处理。说明高浓度氮素添加在一定程度上缓解了植物氮素限制,能够显著促进表层土壤（0-20 cm）中植物细根的生长,但对亚表层土壤（20-40 cm）中细根的影响幅度小于表层土壤。     

3种酰胺类稻田除草剂对克氏原螯虾的急性毒性

[目的] 研究稻虾共作模式条件下,稻田封闭除草剂对克氏原螯虾产生的急性毒性。[方法] 采用半静态试验方法,研究3种酰胺类除草剂（乙草胺、丙草胺和丁草胺）对克氏原螯虾的急性毒性,计算3种酰胺类除草剂对克氏原螯虾的安全浓度,并分析其LC₅₀衰减规律。[结果] 随着暴露时间和除草剂浓度的增加,虾体侧躺,步行足和游泳足活动频率降低,最终死亡。乙草胺对克氏原螯虾的96 h半致死浓度（LC₅₀）和安全浓度（SC）分别为0.0707和0.0146 mL·L^-1;丙草胺对克氏原螯虾的96 h LC₅₀和SC分别为0.0119和0.0021 mL·L^-1;丁草胺对克氏原螯虾的96h LC₅₀和SC分别为0.0073和0.0014 mL·L^-1。乙草胺、丙草胺及丁草胺除草剂LC₅₀随着暴露时间延长呈下降趋势,符合双曲线衰减模型,回归方程分别为：① y₁=2.0840x^-0.7380（R²=0.9973）;② y₂=0.1106x^-0.4930（R²=0.9872）;③ y₃=0.2236x^-0.7480（R²=0.9990）。克氏原螯虾对3种除草剂的敏感性由高到低依次为：丁草胺 > 丙草胺 > 乙草胺。[结论] 乙草胺和丙草胺可在稻田综合种养生产过程中按常规剂量使用,而丁草胺按常规剂量使用可能存在较大的风险。     

武夷山国家公园不同林地土壤呼吸动态变化及其影响因素

探明亚热带山岳型国家公园不同林地利用方式下土壤呼吸（R_s）的动态变化规律以及影响因素,对准确评价和预测该区域以国家公园为主体的自然保护地体系的碳收支具有重要的现实意义。以武夷山国家公园为研究对象,利用Li-8100开路式土壤碳通量测定系统对茶园、锥栗（Castanea henryi（Skam） Rehd.et Wils.）林、马尾松（Pinus massoniana Lamb.）林和裸地的土壤呼吸及近地面气温、土壤温度、土壤湿度、土壤养分和土壤微生物碳（MBC）、氮（MBN）进行测定。结果显示：（1）与近地面气温、土壤温度和土壤湿度相同,不同林地的R_s均呈现夏 > 春 > 秋 > 冬的季节动态,R_s的季节均值按大小排序为茶园（3.10 μmol m^-2 s^-1） > 马尾松（2.96 μmol m^-2 s^-1） > 锥栗（2.32 μmol m^-2 s^-1） > 裸地（1.43 μmol m^-2 s^-1）,锥栗和裸地之间、锥栗与马尾松之间均差异显著（P<0.01）。除马尾松林外,其他林地水热因子（近地面气温、土壤温度和土壤湿度）的单因子二次多项式模型对R_s的拟合度最高。水热因子共同建立的复合模型中,土壤温度、湿度的幂-指数模型对茶园R_s的拟合度较高,土壤温度和土壤湿度能够解释R_s变化的80%,马尾松林的R_s较适用于土壤温度、湿度建立的对数函数模型,而三因子线性模型（进入回归法）对锥栗林和裸地的R_s的拟合度最优,R²分别为0.565和0.281。（2）茶园和锥栗林的碳、氮、磷含量均高于马尾松林和裸地,MBN含量茶园 > 马尾松 > 锥栗 > 裸地。茶园的R_s与全磷（TP）、有效磷（AP）、全钾（TK）、速效钾（AK）含量呈极显著（P<0.01）正相关,马尾松林的R_s受TP、TK、AK含量的影响极显著（P<0.01）,锥栗林的R_s与TK、AK、MBN含量呈现显著（P<0.05）正相关,裸地的R_s受MBN含量影响较为显著（P<0.05）,4种林地土壤呼吸与养分的多元逐步回归方程R²均接近1。综上,茶园和马尾松林土壤呼吸速率较高,且所有林地的土壤呼吸均呈现夏 > 春 > 秋 > 冬的季节动态。温度和湿度与土壤呼吸的相关性强,是水热条件丰富的亚热带山岳地区土壤呼吸季节变化的主导因素,其中武夷山茶园土壤呼吸对水热因子的响应在4种林地中最为敏感。除温度和湿度外,各林地土壤呼吸受P、K元素的影响较大,其中茶园主要受P元素影响,马尾松林地受K元素影响较多。     

六种藓类植物茎的比较解剖学研究

通过对6种藓类植物,即褶叶青藓(Brachythecium salebrosum(Web.et Mohr.)B.S.G.)、湿地匐灯藓(Plagiomnium acutum(Lindb.)Kop.)、侧枝匐灯藓(Plagiomnium maximoviczii(Lindb.)Kop.)、大凤尾藓(Fissidensnobilis Griff.)、大羽藓(Thuidium cymbifolium(Doz.et Molk.)B.S.G.)和大灰藓(Hypnum plumaeforme Wils.)嫩茎和老茎的石蜡切片和显微观察发现,同一藓类植株的嫩茎和老茎,茎结构稳定,不同种藓类植物茎横切面具有不同特征.植物体茎横切面形状、表层细胞的层数、细胞大小和细胞壁厚薄、皮层细胞大小和形状、中轴的有无以及比例等特征可以作为藓类植物的分科分类依据之一.     

Photoregulation of seed germination of wild-type and of an aurea-mutant of tomato

Seed germination of an aurea mutant of tomato ( Lycopersicon esculentum Mill.) is promoted by continuous irradiation with red, far-red or long-wavelength far-red (758 nm) light as well as by cyclic irradiations (5 min red or 5 min far-red/25 min darkness). Far-red light applied immediately after each red does not change the germination behaviour. Seed germination of the isogenic wild-type, cv. UC-105, is promoted by continuous and cyclic red light while it is inhibited by continuous and cyclic far-red light and by continious 758 nm irradiation. Far-red irradiation reverses almost completely the promoting effect of red light. The promoting effect (in the aurea mutant) and the inhibitory effect (in the wild-type) of continuous far-red light do not show photon fluence rate dependency above 20 nmol m⁻² s⁻¹. It is concluded that phytochrome controls tomato seed germination throgh low energy responses in both the wild type and the au mutant. The promoting effect of continuous and cyclic far-red light in the au mutant can be attributed to a greater sensitivity to P_fr.     

Cause of Senescence of Nine Sorts of Flowers

The levels of endogenous phytohormones and respiratory rate in nine sorts of flowers such as Cymbidium faberi Rolfe, Nopalxochia ackermannii Kunth and others were investigated both at full bloom and senescence and meanwhile the effect of exogenous phytohormones on prolonging the blossoms and promoting ethylene production were tested. There is a high content of endogenous ethylene in all the long-lived flowere, about 3–16 folds higer than the short-lived ones. There is a high level of ABA at full blooming flowers of short-lived flowers, in which there is no or only some cytokinins in it, but the ratio of CTK (6BA+zeatin)/ABA is smaller(l.7). The endogenous ABA reached a much higher level at senescence in all nine sorts of flowers, so it is reasonable to consider that it is ABA which plays an important role of regulation in controlling flower's senescence. There is a much higher level of GA3 and zeatin in the long-lived flowers which is not demonstrated in the shortlived ones. The respiratory rate is one of the factors controtling the longevity of flowers, but it does not play a decided role. Application of 6BA and zeatin prolongs distinctly orchid’s longevity, however exogenous IAA through the promotive action on ethylene production, evidently extends the longevity of the flowers of the Nopalxochia ackermannii Kunth.     

龙胆科药用植物化学成分的研究现状

龙胆科植物在我国的分布范围很广,且多数为药用植物,其多数种属的药用植物,至今其化学成分尚未被系统研究。综述了目前龙胆科药用植物的化学成分的研究现状及一般提取方法,对近年来发现的环烯醚萜及裂环烯醚萜类化合物进行了总结,为本科药用植物的更深入研究提供了参考。     

Interconnection of parameters of regulation system of lipid peroxidation and of morphophysiological parameters of mouse liver

A complex analysis of seasonal fluctuations of the mean group parameters of the system of regulation of lipid peroxidation has been performed in liver of Balb/c mice. Association of lipid characteristics and morphophysiological parameters is studied in the Balb/c mouse liver. An inter-connection is revealed between the liver index and the amount of lysoforms of phospholipids, the scale and character of the interconnection differing essentially depending on proportion of phos-phatidylcholine in mouse liver phospholipids.     

The effects of glutamine of the maintenance of embryogenic cultures of Cryptomeria japonica

Summary Embryogenic tissues of sugi (Cryptomeria japonica) were induced on a modified Campbell and Durzan (CD) medium containing 1 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 600 mg l⁻¹ glutamine, and subcultured in the medium of the same composition for over 1 yr. This resulted in a mixed culture of embryogenic and non-embryogenic cells. When embryogenic cells were isolated and cultured independently, their capacity to form embryogenic aggregates was lost. Thus, the non-embryogenic cells present within a mixed culture system were essential to the formation of embryogenic aggregates. When embryogenic tissues were isolated and cultured independently on a high glutamine-containing (2400 mg l⁻¹) medium, dry weights and endogenous levels of glutamine increased, and the tissue could generate a large number of embryogenic aggregates. Amino acid analysis of embryogenic and non-embryogenic cells from the maintenance culture indicated a higher level of glutamine was present in the latter. The high endogenous level of glutamine in the non-embryogenic portion of mixed cell masses may be the supplier of glutamine for maintaining the embryogenic property of the tissues.     

Specificity of action of piperidylcholine derivatives as substrates of cholinesterases of various origin

The review deals with study of enzymologic properties of a novel highly specific acetylcholinesterase substrate, N-(β-acetoxyethyl) piperidinium iodomethylate (“piperidylcholine”), and its 30 derivatives that were tested as effectors of cholinesterases of mammals and various species of Pacific squids. It was proven for the first time that responsible for specificity of action was structure of cyclic ammonium grouping of the alcohol part of molecule of the ester substrate. Analysis of specificity is performed based on enzymatic hydrolysis parameters—activity of catalytic center of cholinesterases and bimolecular constant of the reaction rate that are determined at optimal and low substrate concentrations. Among the specially synthesized group of thioester compounds there is revealed one more highly specific acetylcholinesterase substrate—N-(β-acetoxyethyl) piperidinium.     

Physiological characteristics of various species of strains of carboxydobacteria

Seven strains of aerobic carbon monoxide-oxidizing bacteria (carboxydebacteria) when growing on CO as sole source of carbon and energy had doubling times which ranged from 12–42 h. The activity profiles obtained after discontinuous sucrose density gradient centrifugation indicated that the CO-oxidizing enzymes are soluble and the hydrogenases are membrane-bound in all strains examined. The CO-oxidizing enzymes of Pseudomonas carboxydohydrogena, Pseudomonas carboxydoflava, Comamonas compransoris, and the so far unidentified strains OM2, OM3, and OM4 had a molecular weight of 230,000; that of Achromobacter carboxydus amounted to 170,000. The molecular weights of the CO-oxidizing and H₂-oxidizing enzymes turned out to be identical. The cell sonicates were shown to catalyze the oxidation of both CO and H₂ with methylene blue, thionine, phenazine methosulfate, toluylene blue, dichlorophenolindophenol, cytochrome c or ferricyanide as electron acceptors. Methyl viologen, benzyl viologen, FAD⁺, FMN⁺, and NAD(P)⁺ were not reduced. The spectrum of electron acceptors was identical for all strains tested. Neither free formate, hydrogen nor oxygen gas were involved in the CO-oxidation reaction. Methylene blue was reduced by CO at a 1:1 molar ratio. The results indicate that CO-oxidation by carboxydobacteria is catalyzed by identical or similar enzymes and that the reaction obeys the equation CO+H₂OCO₂+2H⁺+2e^- as previously shown for Pseudomonas carboxydovorans.Dedicated to Otto Kandler remembering almost three decades of enjoyable cooperation     

Modulation of allostery of pyruvate kinase by shifting of an ensemble of microstates

Since the introduction of the concepts of allostery about four decades ago, much advancement has been made in elucidating the structure-function correlation in allostery. However, there are still a number of issues that remain unresolved. In this review we used mammalian pyruvate kinase (PK) as a model system to understand the role of protein dynamics in modulating cooperativity. PK has a triosephosphate isomerase (TIM)(α/β)₈ barrel structural motif. PK is an ideal system to address basic questions regarding regulatory mechanisms about this common (α/β)₈ structural motif. The simplest model accounting for all of the solution thermodynamic and kinetic data on ligand-enzyme interactions involves two conformational states, inactive E^T and active E^R. These conformational states are represented by domain movements. Further studies provide the first evidence for a differential effect of ligand binding on the dynamics of the structural elements, not major secondary structural changes. These data are consistent with our model that allosteric regulation of PK is the consequence of perturbation of the distribution of an ensemble of states in which the inactive E^T and active E^R represent the two extreme end states. Sequence differences and ligands can modulate the distribution of states leading to alterations of functions. The future work includes: defining the network of functionally connected residues; elucidating the chemical principles governing the sequence differences which affect functions; and probing the nature of mutations on the stability of the secondary structural elements, which in turn modulate allostery.