Water Activity Dependence of Lipases in Non-aqueous Biocatalysis

Eleven lipases are tested and it was found that lipases can be divided into three types according to water activity dependence. The first type is lipase that has low water activity dependence and works in a low water activity, its performance changes little with the change of water activity. The optimum water activity is 0.19 and Newlase F (Rhizopus niveus), lipase FAP-15 (Rhizopus oryzae) belong to this type. The second type is lipase that has medium water activity dependence and its performance changes with the change of water activity. Most lipases belong to this type and the optimum water activity in this type is about 0.60. The third type is lipase that has a high water activity dependence and works only in a high water activity (a _w  > 0.75). WGL (wheat germ) belongs to this type and the optimum water activity is 0.90. The relationship between enantioselectivity and water activity is also discussed and the enantioselectivity seems to be independent of water activity. And we also compared the two control methods of water activity, it was found that the method which add solid salt hydrates to the reaction mixture (method II) is more stable and effective throughout the reaction than the method that pre-equilibrate via the vapor phase (method I). The addition concentration of salt hydrates is also investigated and the optimum concentration is 1 g/l.     

Interpretation of the measurement results near the detection limit in gamma-ray spectrometry using Bayesian statistics

The requirement that the true value of an activity cannot be negative is used for the transformation of raw observed values, which can be positive or negative, into the expected activity values. The probability distribution of the activity values is a truncated Gaussian distribution, and the expected value and the variance of the activity values are derived from the observed value and its standard deviation. It has been shown that the standard deviation of the activity values is smaller than the standard deviation of the observed value and that the ratio of the standard deviation of the activity values and the expected value is less than unity. Since the expected activity value is larger than the original observed value, and the standard deviation of the activity values is smaller than the standard deviation of the observed value, the additional information, that the activity cannot be negative, leads to an improvement in the result. However, since the expected activity value depends on the standard deviation of the observed value, conservatively assessed standard deviation lead to a bias of the expected activity values.     

Geographical and vertical distribution of radiocesium levels in coniferous forest soils in Izmir

Preliminary picture of ¹³⁷Cs radioactivity levels in forested areas in and around Izmir is illustrated. Both activity concentrations and activity depositions of ¹³⁷Cs in soil samples were determined. Their values varied from 8.29±0.27 to 445±3.16 Bq.kg⁻¹ (d.w.) and 0.63±0.01 to 11.6±0.08 kBq.m^–2 (d.w.), respectively. It was found that while activity deposition of ¹³⁷Cs is normally distributed, activity concentration of ¹³⁷Cs is log-normally distributed in forest soils and the activity deposition is less variable than the activity concentration. Cesium-137 activities in soils increase with increasing elevation, annual average rainfall and soil organic matter.     

鱼藤酮类衍生物的研究进展

鱼藤酮类衍生物是一类从鱼藤属等植物中提取出来的具有杀虫活性的异黄酮类化合物. 从1932年至今, 已经从植物中提取分离出47种鱼藤酮类化合物. 这一类化合物之所以具有很好的杀虫活性, 是由于对还原型烟酰胺腺嘌呤二核甘酸(NADH)的抑制作用而阻断了线粒体的呼吸. 对天然鱼藤酮类衍生物的结构、活性和合成方面的研究分别进行了概括.     

Involvement of protein kinase C pathway in UVC-stimulated phospholipase D2 activity in Vero 76 cells

Phospholipase D (PLD) activity is known to be related to oxidant-induced cellular signaling and membrane disturbance. Previously, an induction of PLD activity in various cell lines by X-ray irradiation was observed. In this study, we examined the effect of UVC radiation on the PLD activity in Vero 76 cells. At a dose of 10 kJ/m2 of UVC irradiation, the PLD activity was stimulated approximately 10-fold over the basal activity. This UVC-induced PLD activity was found to be dependent on the presence of extracellular calcium and was inhibited by catalase as well as amifostine-an intracellular thiol antioxidant. Pretreatments with Ro32-0432-a selective inhibitor of protein kinase C (PKC)-and downregulation of PKC by preincubation of phorbol 12-myristate 13-acetate significantly inhibited the UVC-induced PLD activity. UVC-stimulated PLD activity was observed only in murine PLD2 (mPLD2)-transfected Vero 76 cells and not in human PLD1 (hPLD1)-transfected cells. Transient incorporation of PKC with mPLD2 and the phosphorylation of mPLD2 by a and b forms of PKC by UVC irradiation were observed. These results suggest that the UVC-stimulated PLD activity in Vero 76 cells is mediated through transient phosphorylation of PLD2 by the translocation of PKC to PLD2.     

Radium in drinking water in Quebec, Canada

Summary The median²²⁶Ra activity found in 216 drinking water samples in Quebec is 14 mBq/l. Only 6% of samples studied have an activity higher than the Maximum Contaminant Level of 111 mBq/l. The detection limit of the method is 4 mBq/l.     

Activity of zeolites in dimethyl sulfide synthesis

Dimethyl disulfide conversion into dimethyl sulfide over various zeolites in an inert medium at atmospheric pressure and T = 190–330°C is reported. A significant activity in dimethyl sulfide formation is shown by the decationized zeolites HNaY and HZSM-5, whose surface has strong protonic and nonprotonic acid sites. Cobalt-containing faujasite is more active than HNaY, and the activity of CoHZSM-5 is comparable with the activity of its decationized counterpart.     

Palladium complexes in concentrated nitrate and acid solutions

A spectrophotometric study of palladium complexation in concentrated nitrate and acid solutions is presented. The water activity of the solutions was fixed to control activity coefficients. The existence of the species PdNO(+)(3), Pd(NO(3))(2) and PdOHNO(3) has been evidenced and their stability was evaluated. An activity diagram for the predominance of soluble palladium species is presented and the precipitation limit is drawn.     

Effect of light on soluble guanylyl cyclase activity in Pharbitis nil seedlings

Cyclic GMP acts as a chemical switch in plant cells to modulate cellular reactions. However, its metabolism has not been extensively explored and is still poorly understood. Previous experiments suggest that an endogenous cGMP system could participate in the mechanism of phytochrome controlled photoperiodic flower induction in Pharbitis nil. In order to gain further information on the role of cGMP, we have begun to study the enzyme of cGMP synthesis. In this article, the presence of the enzyme with guanylyl cyclase (GC) activity in soluble protein fractions of P. nil is reported. A large portion of the enzymatic activity is present in the cotyledons, where enzyme activity amounted to 0.45 pmol cGMP/min/mg protein. The enzyme exhibited a K(m) 0.5mM for GTP. A plot of 1/v versus 1/[GTP] was linear and V(max) was 0.74 pmol cGMP/min/mg protein. It was shown that the anti-sGC antibody recognise a 40 kDa protein. Moreover, the NO-donor, sodium nitroprusside (SNP) and YC-1, as a NO-independent stimulator, enhanced enzyme activity. The NS 2028 (a potent GC inhibitor) treatments provoked a 3-fold reduction of the enzyme activity in comparison to the untreated fractions. Furthermore, the influence of light on GC activity was analysed. It was noted that cGMP level increased in cool white light, and darkness inhibited enzyme activity. Exposure to blue light acts to stimulate cGMP formation, whereas in red light a rapid decrease in GC activity was observed that returned to the high level when far-red light was applied after the red light treatment. The results presented in this work strongly argue that an enzyme with guanylyl cyclase activity is present in P. nil organs and its activity is controlled by light via the photoreceptors-dependent pathways.     

Activity coefficients in an ionic micellar system

The average activity coefficients of ionic surfactants as a whole and their monomeric forms are compared. The concept of an aggregative activity coefficient is introduced.     

Effect of Phase Composition and Acidity on the Catalytic Properties of Molecular Sieves Containing Zirconium in Oxidative Reactions and in the Reduction of Nitrogen Monoxide

Comparative investigations of the catalytic activity of molecular sieves of different types containing zirconium showed that Zr-pentasil, doped with cobalt oxide, had considerable oxidation activity with respect to nitrogen monoxide, but SCR activity of these samples is connected to the acidity of the surface, which is necessary to activate methane to reduce nitrogen monoxide. Mesoporous molecular sieves, doped with cobalt oxide, chromium and cerium oxides, did not appear to have catalytic activity with respect to selective reduction of nitrogen monoxide with methane or propane–butane mixtures. This is connected with the effect of structural factors and the absence of acidic B-centers.     

Activity Coefficients in the Surface Phase of Liquid Mixtures

A novel equation for evaluating surface activity coefficients is obtained from a recent thermodynamic formalism describing the surface phase of liquid mixtures. The input quantities are the surface tension, bulk activity coefficients and pure constituent thermophysical properties. It is demonstrated thermodynamically that the order of magnitude of each component surface and bulk activity coefficients must be the same. This order is intrinsically associated with the sign of excess surface tension. Reliable activity coefficients of ethanol and water in the surface phase of their mixtures are computed and reported for the first time, by using literature data for the required input quantities. It is shown that the so‐called transferring method for estimating surface activity coefficients is severely flawed, because it leads to contradictory values of predicted excess surface tensions depending on which component this prediction is based.     

荧光光度法测定血清中碱性磷酸酶

合成了一种新的底物水杨酸磷酸酯 (SP),用于荧光光度法测定血清中碱性磷酸酶(ALP)活力.在37.0 ℃的Tris-HCl缓冲液(pH 9.0)条件下, 碱性磷酸酶作用于荧光底物SP,水解生成强荧光产物水杨酸(SA),生成的SA的量与参与反应的ALP 的活力成正比.据此建立了荧光光度法测定血清中碱性磷酸酶活力的新方法.测定碱性磷酸酶的线性范围是0.03～6.00 U/L,检测限为7.04 mU/L.本方法适用于血清中碱性磷酸酶的测定.测定结果与临床上常用的以对硝基苯磷酸酯为底物的分光光度法相比,无显著性差异.     

Solute retention in the stationary phase of a liquid-solid chromatographic system

Summary Utilizing the UNIFAC group model of activity coefficients the retention behaviour of a solute in the stationary phase of a liquid-solid chromatographic system is studied. By comparison of experimentally observed capacity ratios and calculated activity coefficients of solutes in the mobile phase, varying the concentration of a polar moderator, it is shown that the calculated activity coefficients in the stationary phase fit very well the equation formally identical with the Langmuir function. Comparison of activity coefficients in the mobile and the stationary phase proves equivalence between the solvent interaction and the competition theory.     

Activity coefficients of ions in sodium halide solutions: Critical remarks

The fundamentals of an experimental method proposed by Zhuo et al. [1], to determine activity coefficients of sodium and halide ions in sodium halide solutions, are critically examined. It is shown that this method relies on a key hypothesis, which proves to be incorrect, about the liquid junction potential, whose value is assumed not to change when the concentration of the sample solution is changed. The direct consequence of this assumption is that results that are interpreted as the activity coefficients of sodium and halide ions are, instead, conventional values, which only depend on the mean activity coefficients and transport numbers, and have no connection with the activity coefficients of the respective ions.     

Mitotic and amitotic cell replication in malignant melanoma: the role of subdivisional cell replication

It is widely assumed that significant mitotic activity is typical of malignant melanoma and many believe that significant mitotic activity is essential for this diagnosis. We have studied mitotic activity in 205 malignant melanomas and have found that mitotic activity is often minimal or absent, even in malignant melanomas which have recurred or metastasized. Based on our previous work suggesting that new cells can form from nucleoli via nucleolar stalks, we also studied nucleolar stalks in our cases. These were present in greater numbers than mitoses and help explain the anomaly of infrequent mitoses in a highly malignant neoplasm.     

Ethanol elimination in regenerating rat liver: the roles of alcohol dehydrogenase and acetaldehyde.

The rate of ethanol elimination in vivo was studied with rats in which the energy consumption of the liver was increased by partial hepatectomy. Immediately after partial hepatectomy the activity of alcohol dehydrogenase in the liver remnant was not changed from that of the livers of sham-operated controls, but the rate of ethanol removal was significantly faster. Twenty-four h after the partial hepatectomy the activity of alcohol dehydrogenase was only 48 % of the activity measured in unoperated control rats. Therefore it is concluded that in normal liver the activity of ADH is in excess. In partially hepatectomized rats the rate of ethanol elimination was linearly correlated with the activity of alcohol dehydrogenase, which suggests that when the rate of NADH reoxidation is markedly increased, as in regenerating rat liver, the rate of ethanol elimination may be limited by the activity of alcohol dehydrogenase. The activity of aldehyde dehydrogenase and the concentration of acetaldehyde in the tail blood were not significantly changed from the level of unoperated rats during oxidation of ethanol.     

胆色素类化合物光学活性及其立体化学研究进展

本文综述了20 年来胆色素光学活性及其立体化学的研究进展, 着重讨论了分子内和分子间相互作用对色素构象的选择性及其光活性的影响。对研究前景进行了展望。     

论科学探究中的"科学问题"

“科学问题”是科学探究活动的要素,并贯穿于探究活动的始终。在教学活动中,并不是所有的科学问题都需要去探究,而应该选择有探究价值的科学问题进行探究。     

Activity of water in aqueous systems; a frequently neglected property

In this critical review, the significance of the term 'activity' is examined in the context of the properties of aqueous solutions. The dependence of the activity of water(l) at ambient pressure and 298.15 K on solute molality is examined for aqueous solutions containing neutral solutes, mixtures of neutral solutes and salts. Addition of a solute to water(l) always lowers its thermodynamic activity. For some solutes the stabilisation of water(l) is less than and for others more than in the case where the thermodynamic properties of the aqueous solution are ideal. In one approach this pattern is accounted for in terms of hydrate formation. Alternatively the pattern is analysed in terms of the dependence of practical osmotic coefficients on the composition of the aqueous solution and then in terms of solute-solute interactions. For salt solutions the dependence of the activity of water on salt molalities is compared with that predicted by the Debye-Hückel limiting law. The analysis is extended to consideration of the activities of water in binary aqueous mixtures. The dependence on mole fraction composition of the activity of water in binary aqueous mixtures is examined. Different experimental methods for determining the activity of water in aqueous solutions are critically reviewed. The role of water activity is noted in a biochemical context, with reference to the quality, stability and safety of food and finally with regard to health science.