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Beavan M. Zawadzki B. Dronicik R. Lawford H. Fein J. 《Applied biochemistry and biotechnology》1989,20(1):319-326
Applied Biochemistry and Biotechnology - Z.mobilis (ATCC 29191) produced ethanol in significantly greater yield thanS. cerevisiae, (0.49 vs 0.45 g ethanol/g glucose entering the system), in... 相似文献
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Recently, a novel enzymatic method was developed for determination of homocysteine. This method utilizes the electrochemical hydrogen sulfide sensor along with methionine α,γ‐lyase to accomplish the fast, accurate, sensitive and selective measurements. As a continuation of this work, another enzyme, homocysteine α,γ‐lyase, was used and the parallel experiments of using both enzymes were carried out against the effect of pH, sensitivity, linearity, and interferences, in an intended comparison between these two enzymes. The excellent linearity of amperometric currents against homocysteine concentrations, high sensitivities and low detection limits for both enzymes reconfirmed that the electrochemical method is superior over other analytical means. The high enzymatic activity of methionine α,γ‐lyase surpassing homocysteine α,γ‐lyase endowed the former higher sensitivity, lower detection limit and faster response than the latter, suggesting methionine α,γ‐lyase a better candidate for homocysteine measurement by electrochemical method. The differences between these two enzymes on the trends of response time and sensitivity at different pH environments, reactivity toward several forms of homocysteine as well as on the interference from several agents were also addressed and discussed. 相似文献
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BIT Numerical Mathematics - 相似文献
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Burton Fein Murray Schacher 《Transactions of the American Mathematical Society》2000,352(9):4355-4369
Let be either a number field or a field finitely generated of transcendence degree over a Hilbertian field of characteristic 0, let be the rational function field in one variable over , and let . It is known that there exist infinitely many such that the specialization induces a specialization , where has exponent equal to that of . Now let be a finite extension of and let . We give sufficient conditions on and for there to exist infinitely many such that the specialization has an extension to inducing a specialization , the residue field of , where has exponent equal to that of . We also give examples to show that, in general, such need not exist.
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Throughour this paper G denotes an abelian divisible torsion group. It is not unreasonable to conjecture that such a G must occur as the Brauer group B(K) of some field K. Some evidence to support this conjecture is provided in [3]; it is proved there that if G is countable then G ? B(K) for some K algebraic over the rational field Q [3, Theorem 2]. In this note we provide still more evidence in support of htis conjecture. 相似文献
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DC Muddiman AP Null JC Hannis 《Rapid communications in mass spectrometry : RCM》1999,13(12):1201-1204
Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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Bacterial surface adsorption reactions are influenced by electric field effects caused by changes in ionic strength; however, existing datasets are too sparse to definitively constrain these differences or to determine the best way to account for them using thermodynamic models. In this study, we examine the ionic strength dependence of proton and metal adsorption onto the surfaces of Pseudomonas mendocina and Pseudomonas putida by conducting proton, Cd(II), Pb(II), and Sr(II) adsorption experiments over the ionic strength range of 0.001 to 0.6 M. Chosen experimental results are thermodynamically modeled using a non-electrostatic approach, a diffuse layer model (DLM), and a triple-layer model (TLM). The results demonstrate that bacterial surface electric field effects are negligible for proton, Cd, and Pb adsorption onto P. putida and P. mendocina, and that the discrete site non-electrostatic model developed in this study is adequate for describing these reactions. The extent of Sr adsorption is influenced by changes in the bacterial surface electric field; however, the non-electrostatic model better describes Sr adsorption behavior than the DLM or TLM. The DLM and TLM greatly overpredict the effect of the electric field for all adsorption reactions at all ionic strengths tested. 相似文献
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KM Clauwaert Van Bocxlaer JF HJ Major JA Claereboudt WE Lambert Van den Eeckhout EM Van Peteghem CH De Leenheer AP 《Rapid communications in mass spectrometry : RCM》1999,13(14):1540-1545
This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd. 相似文献