Analysis of medaka cytochrome P450 3A homotropic and heterotropic cooperativity

We have previously demonstrated that medaka CYP3A is associated with metabolism of several endobiotics including steroids and bile acids. In this study, we demonstrate that medaka CYP3A catalysis exhibits unusual kinetic behaviors consistent with allosteric interaction which cannot be described by hyperbolic kinetic models. Using 7-benzyloxy-4-(trifluoromethyl)-coumarin (BFC) and nonylphenol as CYP3A substrates, we describe both homotropic and heterotropic cooperative interactions. Given the role of CYP3A in maintaining the homeostatic balance for numerous endobiotics, enzymatic activation/inhibition by endocrine disruptors (EDCs) represents a putative (non-genomic) mechanism for endocrine disruption.     

Biogeochemical cycles of carbon, sulfur, and free oxygen in a microbial mat

Complete budgets for carbon and oxygen have been constructed for cyanobacterial mats dominated by Microcoleus chthonoplastes from the evaporating ponds of a salt works located in Guerrero Negro, Baja California Sur, Mexico. Included in the budget are measured rates of O2 production, sulfate reduction, and elemental exchange across the mat/brine interface, day and night, at various temperatures and times of the year. We infer from this data the various sinks for O2, as well as the sources of carbon for primary production. To summarize, although seasonal variability exists, a major percentage of the O2 produced during the day did not diffuse out of the mat but was used within the mat to oxidize both organic carbon and the sulfide produced by sulfate reduction. At night, most of the O2 that diffused into the mat was used to oxidize sulfide, with O2 respiration of minor importance. During the day, the internal mat processes of sulfate reduction and O2 respiration generated as much or more inorganic carbon (DIC) for primary production as diffusion into the mat. Also, oxygenic photosynthesis was the most important process of carbon fixation, although anoxygenic photosynthesis may have been important at low light levels during some times of the year. At night, the DIC lost from the mat was mostly from sulfate reduction. Elemental fluxes across the mat/brine interface indicated that carbon with an oxidation state of greater than zero was taken up by the mat during the day and liberated from the mat at night. Overall, carbon with an average oxidation state of near zero accumulated in the mat. Both carbon fixation and carbon oxidation rates varied with temperature by a similar amount. These mats are thus closely coupled systems where rapid rates of photosynthesis both require and fuel rapid rates of heterotrophic carbon oxidation.     

Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments

Isotope fractionation during sulfate reduction by natural populations of sulfate-reducing bacteria was investigated in the cyanobacterial microbial mats of Solar Lake, Sinai and the sediments of Logten Lagoon sulfuretum, Denmark. Fractionation was measured at different sediment depths, sulfate concentrations, and incubation temperatures. Rates of sulfate reduction varied between 0.1 and 37 micromoles cm-3 d-1, with the highest rates among the highest ever reported from natural sediments. The depletion of 34S during dissimilatory sulfate reduction ranged from 16% to 42%, with the largest 34S-depletions associated with the lowest rates of sulfate reduction and the lowest 34S-depletions with the highest rates. However, at high sulfate reduction rates (>10 micromoles cm-3 d-1) the lowest fractionation was 20% independent of the rates. Overall, there was a similarity between the fractionation obtained by the natural populations of sulfate reducers and previous measurements from pure cultures. This was somewhat surprising given the extremely high rates of sulfate reduction in the experiments. Our results are explained if we conclude that the fractionation was mainly controlled by the specific rate of sulfate reduction (mass cell-1 time-1) and not by the absolute rate (mass volume-1 time-1). Sedimentary sulfides (mainly FeS2) were on average 40% depleted in 34S compared to seawater sulfate. This amount of depletion was more than could be explained by the isotopic fractionations that we measured during bacterial sulfate reduction. Therefore, additional processes contributing to the fractionation of sulfur isotopes in the sediments are indicated. From both Solar Lake and Logten Lagoon we were able to enrich cultures of elemental sulfur-disproportionating bacteria. We suggest that isotope fractionation accompanying elemental sulfur disproportionation contributes to the 34S depletion of sedimentary sulfides at our study sites.     

镜泊湖地区水体的同位素、元素地球化学特征及地下热水储存状态分析

依据镜泊湖地区水体的同位素、水化学及微量元素中子活化分析资料，详细阐述了各采样点水体的来源、补给相对高程和它们之间可能的水力联系，以及有关的地热信息；分析了区内地热资源的有利地质背景条件研究区地处深大断裂及岩浆喷发带，火山喷发一直延续至第四纪全新世，有充分的热源供给；区内上部为较厚的玄武岩覆盖，有利于储存地热；下部白垩系上统为主要含水层，发现有广泛分布的典型木／岩热蚀变产物——斜发沸石，进而证明存在地下热水的可能性。     

贡嘎山海螺沟冰川径流水文规律的同位素示踪研究

应用同位素地球化学的基本原理和示踪技术, 对贡嘎山海螺沟冰川河源区和干流的不同区段, 不同时域径流的组成特点及其水文动态变化规律进行分析研究.结果表明: 贡嘎山海螺沟冰川河源区水的组成, 不同季节、不同时段(早、晚)有明显的变化. 夏季晚上的水大约有82.4%是来自冰川区的水, 17.6%为非冰川区的径流; 早晨中的水来自冰川区的占74.6%, 非冰川区径流占25.4%. 冰川消融水的最大可占总水量的6.9%～7.8%左右. 在冬季时段, 冰舌末端排泄水(BCH-1)和冰川水文站(HLG-6)径流的同位素组成均低于底部冰川冰(BCB-2: -16.639‰), 显示出严重同位素不平衡的特点, 反映了冬季底部冰川消融水在源区水(BCH-1)中的贡献已达很低的程度, 而代之以冰川上部占主导优势的雨雪水. 这意味着在冬季当地冰川的退缩速度与夏季相比有明显减慢的趋势. 示踪表明, 在冰川水文站附近区域内存在水的渗漏, 夏季可能延伸到倒中桥(HLG-13采样点上方)一带, 下渗水通过地下通道, 到杉树坪(HLG-2采样点)邻近的区域回补到河道内.     

四川米易垭口地区前震旦纪五马箐组与其侵入岩体的锆石U-Pb年代学、Lu-Hf同位素特征及其地质意义SCIEI北大核心CSCD

在扬子板块西缘断续分布有多套变质沉积岩系,厘定区内不同岩石单元的时代对于探讨扬子西缘的构造演化具有重要意义。本文对出露于扬子板块西缘米易垭口地区的五马箐组变沉积岩以及侵入其中的片麻状黑云二长花岗岩体进行了锆石LA-ICP-MS U-Pb定年和Lu-Hf同位素分析。结果表明:区内五马箐组的沉积时代介于1.19~1.01Ga,其地层归属为会理群而非康定群,位于五马箐组之下的“冷竹关组”并非变沉积地层而是一套片麻状黑云二长花岗岩体。五马箐组碎屑锆石年龄存在~1.56Ga、~2.50Ga两个主要峰值以及~1.43Ga、~1.68Ga、~1.87Ga、~2.32Ga、~2.68Ga五个次要峰值,推断其物质来源主要为扬子板块西南缘的撮科杂岩、隐伏的或还暂未发现的太古代基底岩石、同时期岩浆岩和早期变沉积岩的再循环。碎屑锆石的ε_(Hf)(t)值在~1.7Ga发生了显著变化,暗示扬子板块西缘的构造体制由陆壳汇聚向裂谷活动转变,且在~1.56Ga处于裂谷岩浆活动的峰期。花岗岩体正的ε_(Hf)(t)值反映出扬子板块西缘在~1.0Ga有一次新生陆壳生长事件,可能是格林威尔造山后的伸展塌陷构造背景下裂谷岩浆活动的产物。     

EFFECTS OF RIVER NETWORK WORKS AND SOIL CONSERVATION MEASURES ON RESERVOIR SILTATION

Knowledge of the morphological dynamics of a water course is essential for management of reservoir siltation. With an example of sedimentation in a reservoir in Basilicata, Italy, this paper demonstrates the effect on reservoir siltation of the hydraulic works, which are aimed to reduce sediment transport along the fluvial network and to prevent part of the sediment discharge from reaching the lake. The effect depends on the river type and on the the geological features of river basin slopes. The paper also shows how mass erosion can significantly contribute to development of reservoir siltation. Finally, preliminary results are provided about the time needed for river training works to be effective.