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1. chinaXiv:201810.00187 [pdf]

Application and verification of simultaneous determination of cellulose ?13C and ?18O in Picea shrenkiana tree rings from northwestern China using the high-temperature pyrolysis method

XU Guobao; LIU Xiaohong; SUN Weizhen; CHEN Tuo; ZHANG Xuanwen; ZENG Xiaomin; WU Guoju; WANG Wenzhi; QIN Dahe
Subjects: Geosciences >> History of Geosciences

Stable isotopes in tree-ring cellulose provide important data in ecological, archaeological, and paleoenvironmental researches, thereby, the demand for stable isotope analyses is increasing rapidly. Simultaneous measurement of cellulose ?13C and ?18O values from tree rings would reduce the cost of isotopic commodities and improve the analytical efficiency compared with conventional separate measurement. In this study, we compared the ?13C and ?18O values of tree-ring ?-cellulose from Tianshan spruce (Picea schrenkiana) in an arid site in the drainage basin of the Urumqi River in Xinjiang of northwestern China based on separate and simultaneous measurements, using the combustion method (at 1050°C) and the high-temperature pyrolysis method (at 1350°C and 1400°C). We verified the results of simultaneous measurement using the outputs from separate measurement and found that both methods (separate and simultaneous) produced similar ?13C values. The two-point calibrated method improved the results (range and variation) of ?13C and ?18O values. The mean values, standard deviations, and trends of the tree-ring ?13C obtained by the combustion method were similar to those by the pyrolysis method followed by two-point calibration. The simultaneously measured ?18O from the pyrolysis method at 1400°C had a nearly constant offset with that the pyrolysis method at 1350°C due to isotopic-dependence on the reaction temperature. However, they showed similar variations in the time series. The climate responses inferred from simultaneously and separately measured ?13C and ?18O did not differ between the two methods. The tree-ring ?13C and ?18O values were negatively correlated with standardized precipitation evapotranspiration index from May to August. In addition, the ?18O was significantly correlated with temperature (positive), precipitation (negative), and relative humidity (negative) from May to August. The tree-ring ?13C and ?18O values determined simultaneously through the high-temperature pyrolysis method could produce acceptable and reliable stable isotope series. The simultaneous isotopic measurement can greatly reduce the cost and time requirement compared with the separate isotopic measurement. These results are consistent with the previous studies at humid sites, suggesting that the simultaneous determination of ?13C and ?18O in tree-ring ?-cellulose can be used in wide regions.

submitted time 2018-10-29 Cooperative journals:《Journal of Arid Land》 Hits4475Downloads1377 Comment 0

2. chinaXiv:201605.01808 [pdf]

Significant Expansion of Fluorescent Protein Sensing Ability through the Genetic Incorporation of Superior Photo-Induced Electron-Transfer Quenchers

Liu, Xiaohong; Jiang, Li; Li, Jiasong; Wang, Li; Zhou, Qing; Lv, Xiaoxuan; Gong, Weimin; Wang, Jiangyun; Lu, Yi; Lu, Yi; Yu, Yang
Subjects: Biology >> Biophysics

Photo-induced electron transfer (PET) is ubiquitous for photosynthesis and fluorescent sensor design. However, genetically coded PET sensors are underdeveloped, due to the lack of methods to site-specifically install PET probes on proteins. Here we describe a family of acid and Mn(III) turn-on fluorescent protein (FP) sensors, named iLovU, based on PET and the genetic incorporation of superior PET quenchers in the fluorescent flavoprotein iLov. Using the iLovU PET sensors, we monitored the cytoplasmic acidification process, and achieved Mn(III) fluorescence sensing for the first time. The iLovU sensors should be applicable for studying pH changes in living cells, monitoring biogentic Mn(III) in the environment, and screening for efficient manganese peroxidase, which is highly desirable for lignin degradation and biomass conversion. Our work establishes a platform for many more protein PET sensors, facilitates the de novo design of metalloenzymes harboring redox active residues, and expands our ability to probe protein conformational dynamics.

submitted time 2016-05-18 Hits4183Downloads2052 Comment 0

3. chinaXiv:201605.01485 [pdf]

Synthetic Model of the Oxygen-Evolving Center: Photosystem II under the Spotlight

Hu, Cheng; Liu, Xiaohong; Wang, Jiangyun; Yu, Yang
Subjects: Biology >> Biophysics >> Biochemistry & Molecular Biology

The oxygen-evolving center (OEC) in photosystem II catalyzes a water splitting reaction. Great efforts have already been made to artificially synthesize the OEC, in order to elucidate the structure-function relationship and the mechanism of the reaction. Now, a new synthetic model makes the best mimic yet of the OEC. This recent study opens up the possibility to study the mechanism of photosystem II and photosynthesis in general for applications in renewable energy and synthetic biology.

submitted time 2016-05-12 Hits2255Downloads1240 Comment 0

4. chinaXiv:201605.01451 [pdf]

A Designed Metalloenzyme Achieving the Catalytic Rate of a Native Enzyme

Liu, Xiaohong; Wang, Jiangyun; Yu, Yang; Lu, Yi; Cui, Chang; Petrik, Igor D.; Lu, Yi
Subjects: Biology >> Biophysics

Terminal oxidases catalyze four-electron reduction of oxygen to water, and the energy harvested is utilized to drive the synthesis of adenosine triphosphate. While much effort has been made to design a catalyst mimicking the function of terminal oxidases, most biomimetic catalysts have much lower activity than native oxidases. Herein we report a designed oxidase in myoglobin with an O-2 reduction rate (52 s(-1)) comparable to that of a native cytochrome (cyt) cbb(3) oxidase (SO s(-1)) under identical conditions. We achieved this goal by engineering more favorable electrostatic interactions between a functional oxidase model designed in sperm whale myoglobin and its native redox partner, cyt b(5), resulting in a 400-fold electron transfer (ET) rate enhancement. Achieving high activity equivalent to that of native enzymes in a designed metalloenzyme offers deeper insight into the roles of tunable processes such as ET in oxidase activity and enzymatic function and may extend into applications such as more efficient oxygen reduction reaction catalysts for biofuel cells.

submitted time 2016-05-12 Hits2091Downloads1147 Comment 0

5. chinaXiv:201605.01273 [pdf]

Ultrafast Photoinduced Electron Transfer in Green Fluorescent Protein Bearing a Genetically Encoded Electron Acceptor

Lv, Xiaoxuan; Hu, Cheng; Gao, Feng; Li, Jiasong; Liu, Xiaohong; Deng, Kai; Zheng, Peng; Gong, Weimin; Wang, Jiangyun; Lv, Xiaoxuan; Hu, Cheng; Gao, Feng; Li, Jiasong; Liu, Xiaohong; Deng, Kai; Zheng, Peng; Gong, Weimin; Wang, Jiangyun; Zhou, Meng; Xia, Andong
Subjects: Biology >> Biophysics

Electron transfer (ET) is widely used for driving the processes that underlie the chemistry of life. However, our abilities to probe electron transfer mechanisms in proteins and design redox enzymes are limited, due to :the lack of methods to site-specifically insert electron acceptors into proteins in vivo. Here we describe the synthesis and genetic incorporation of 4-fluoro-3-nitrophenylalanine (FNO(2)Phe), which has similar reduction potentials to NAD(P)H and ferredoxin, the most important biological reductants. Through the genetic incorporation of FNO2Phe into green fluorescent:protein (GFP) and femtosecond transient absorption measurement, we show that photoinduced electron transfer (PET) from the GFP chromophore to FNO2Phe occurs very fast (within 11 ps), which is comparable to that of the first electron transfer step in photosystem I, from P700* to A(0). This genetically encoded, low-reduction potential unnatural amino acid (UAA) can significantly in-Trove our ability to investigate electron transfer mechanisms in complex reductases and facilitate the design of miniature proteins that mimic their functions.

submitted time 2016-05-11 Hits1797Downloads1030 Comment 0

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