Multiple forms of xylose reductase in Candida intermedia: comparison of their functional properties using quantitative structure-activity relationships, steady-state kinetic analysis, and pH studies

The xylose-fermenting yeast Candida intermedia produces two isoforms of xylose reductase: one is NADPH-dependent (monospecific xylose reductase; msXR), and another is shown here to prefer NADH approximately 4-fold over NADPH (dual specific xylose reductase; dsXR). To compare the functional properties of the isozymes, a steady-state kinetic analysis for the reaction d-xylose + NAD(P)H + H(+) <--> xylitol + NAD(P)(+) was carried out and specificity constants (k(cat)/K(aldehyde)) were measured for the reduction of a series of aldehydes differing in side-chain size as well as hydrogen-bonding capabilities with the substrate binding pocket of the enzyme. dsXR binds NAD(P)(+) (K(iNAD+) = 70 microM; K(iNADP+) = 55 microM) weakly and NADH (K(i) = 8 microM) about as tightly as NADPH (K(i) = 14 microM). msXR shows uniform binding of NADPH and NADP(+) (K(iNADP+) approximately K(iNADPH) = 20 microM). A quantitative structure-activity relationship analysis was carried out by correlating logarithmic k(cat)/K(aldehyde) values for dsXR with corresponding logarithmic k(cat)/K(aldehyde) values for msXR. This correlation is linear with a slope of approximately 1 (r (2) = 0.912), indicating that no isozyme-related pattern of substrate specificity prevails and aldehyde-binding modes are identical in both XR forms. Binary complexes of dsXR-NADH and msXR-NADPH show the same macroscopic pK of approximately 9.0-9.5, above which the activity is lost in both enzymes. A lower pK of 7.4 is seen for dsXR-NADPH. Specificity for NADH and greater binding affinity for NAD(P)H than NAD(P)(+) are thus the main features of enzymic function that distinguish dsXR from msXR.     

Chlorinated dibenzo-p-dioxin and dibenzofuran concentrations in beef animals from a feeding study

Four calves were fed polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans for 120 days at levels somewhat higher than what may be found in forage near some waste incinerators and manufacturing plants. Four calves were fed identical diets but without the chemicals. Using bioelectrical impedance measurements of total body fat, 30-50% of the dosed 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, and 2,3,4,7,8-PeCDF was estimated to be retained by the animals. Although these same congeners were bioconcentrated in adipose tissue (BCF approximately 10), consumer products such as ribeye showed concentrations less than what were found in the animal feed (BCF approximately 0.1). Distribution of the dioxins and furans into various lipid compartments appeared to be rather uniform in back fat, perirenal fat, and ribeye for tetra to hexa congeners. Ribeye, serum, and liver lipids had higher concentrations of the higher chlorinated congeners, due in part to not reaching a steady state. An unexpected source of dioxin and furan contamination was discovered during the experiment, resulting in the control animals having concentrations of some congeners that were equal to or in some cases greater than those of the dosed animals. Pentachlorophenol-treated wood components in the pole barn where the feeding experiment was conducted were found to have contributed to the animals' exposure.     

Establishing of ‘Reference Plant’ for inorganic characterization of different plant species by chemical fingerprinting

The enormous amount of analytical data produced in environmental trace element research require beside a high degree of quality control a basis for comparability of single analytical values. The establishment of ‘Reference Plant’, comparable to the already existing ‘Reference Man’ by the International Commission of Radiological Protection (ICRP), can be a useful tool for this type of chemical ‘fingerprinting’. In this paper, various fingerprints of different plant species will be discussed and their comparability demonstrated.     

Effects of Lime and Fertilizer Application on Soil Solution Composition in an Acid Sandy Forest Soil

In a 40 year old pine stand, soil solution was collected continuously with suction cups from 50 and 200 cm depth over a 42-month period following the surface application of lime and K/Mg-fertilizer. K and Mg showed a much higher mobility than Ca, which hardly increased in 200 cm depth even after 42 months. After an initial nitrate peak, concentrations decreased but remained elevated throughout the entire study period. In 200 cm, Al-, Mn, and Cd-concentrations increased due to exchange processes in the top-soil. Continuously elevated sulfate concentrations in 200 cm indicate S-mineralisation from humus decomposition.     

Pharmacological studies in an herbal drug combination of St. John's Wort (Hypericum perforatum) and passion flower (Passiflora incarnata): in vitro and in vivo evidence of synergy between Hypericum and Passiflora in antidepressant pharmacological models

Extracts of Hypericum, Passiflora and Valeriana are used for the treatment of mild depression and anxiety. We were interested whether a combination of Hypericum and Passiflora exerts comparable effects to Hypericum alone. We used two well-established models for investigating extracts for their anti-depressant activity, namely the effects on synaptic uptake of serotonin and the forced-swimming-test. We show here for the first time, that Passiflora significantly enhances the pharmacological potency of Hypericum in both models. Our data suggest that anti-depressive therapeutic effects of Hypericum are possible with lower doses, when it is combined with Passiflora, than with mono-preparations of Hypericum.     

Two-year dynamics of foliage labelling in 8-year-old <Emphasis Type="Italic">Pinus pinaster</Emphasis> trees with <Superscript>15</Superscript>N, <Superscript>26</Superscript>Mg and <Superscript>42</Superscript>Ca—simulation of Ca transport in xylem using an upscaling approach

• Introduction   

Atmospheric deposition is an important input of major nutrients into forest ecosystems. The long-term goal of this work was to apply stable isotope methodology to assess atmospheric nutrient deposition in forest systems.     

陕北黄土高原森林植被的性质和当前森林培育的策略

对比和分析了前人对陕北黄土高原植被的研究成果后认为陕北黄土高原的阔叶栎林为主的森林界限截止于渭北黄土高原北部,即陇县、彬县、宜君、铜川、黄龙一线。经过植被破坏和土壤侵蚀后土壤基质已经严重旱化和贫瘠化,通过重建植被土壤基质是可以逐步恢复的。植被的重建应该首选择先锋植物种类,造林后应及时进行改造,使其向接近该区天然林(植被)的方向发展,并需要建立一套可持续的森林经营体系。     

Fluctuations of element concentrations during the growing season of Polytrichum formosum (Hedw.)

Fourteen elements (Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Ni, Pb, Sr, Ti, and Zn) were quantitatively determined by AES/ICP in aboveground parts of the endohydric moss Polytrichum formosum (Hedw.) after sampling over regular intervals from 1985 to 1987. With the exception of K, Mg, and Zn all elements showed a large continuous fluctuation (> 30%) during the growing season. Four different patterns of seasonal variation were found: (1) large seasonal variations of element concentrations (～80%) with maximum concentrations in winter and lowest concentrations in the summer months (Al, Fe, Cr, Mg, Pb, and Ti), (2) smaller seasonal variations (～50%) with maximum concentrations in winter and lowest concentrations in summer (Ba, Ca, Cd, Cu, Sr), (3) slight seasonal variations (～30%) with maximum concentrations in the summer (K), and (4) slight seasonal changes (～30%) with maximum concentrations in the winter (Mg and Zn). The relative biological variance of element concentrations between 9 different stands of Polytrichum formosum decreases in the following sequence: Ti, Al, Pb, Fe, Cr, Ni, Ba, Ca, Cu, Cd, K, Mg, Sr, Zn. The relative biological variance of individual elements is generally lower than the variance in element concentrations caused by seasonal changes. Because of its high biological variance for most elements investigated (seasonal as well as between different stands of Polytrichum formosum) this moss should only be used as a passive bioindicator, if all other environmental parameters are standardized.