Functional conversion between A-type and delayed rectifier K+ channels by membrane lipids

Voltage-gated potassium (Kv) channels control action potential repolarization, interspike membrane potential, and action potential frequency in excitable cells. It is thought that the combinatorial association between distinct alpha and beta subunits determines whether Kv channels function as non-inactivating delayed rectifiers or as rapidly inactivating A-type channels. We show that membrane lipids can convert A-type channels into delayed rectifiers and vice versa. Phosphoinositides remove N-type inactivation from A-type channels by immobilizing the inactivation domains. Conversely, arachidonic acid and its amide anandamide endow delayed rectifiers with rapid voltage-dependent inactivation. The bidirectional control of Kv channel gating by lipids may provide a mechanism for the dynamic regulation of electrical signaling in the nervous system.     

Determination of 28 Elements in Aquatic Moss Fontinalis Antipyretica Hedw. and Water from the Upper Reaches of the River Nysa (CZ,D), by ICP-MS,ICP-OES and AAS

The concentrations of 28 elements in samples of the bryophyte F. antipyretica Hedw collected from various sites on the upper reaches of the River Nysa and its main tributaries were determined. These results were compared with similar analyses of water samples collected at the same sites. So, it was possible to determine the elemental composition of the water both directly and indirectly, using a bioindicator organism. Analyses were carried out using different instrumental techniques (ICP-MS, ICP-OES, AAS), some elements being analysed by both ICP-MS and ICP-OES. Functional regression analysis showed that for some of these elements, namely Al, Ba, Fe, Sr and Ti in moss, and Ba, Ca and Zn in water samples, there was no significant difference (p < 0.05) in the concentrations determined by both techniques. The coefficients of correlation moss/water for each element were calculated, but they were in general low. However the coefficients of correlation between different elements were in general good. Finally, the elemental concentrations in the aquatic moss were also used to assess the level of contamination in the area of study, through the calculation of CF (Contamination Factor) values.     

Priming effects in soil size fractions of a podzol Bs horizon after addition of fructose and alanine

It is well known that the addition of easily available substrates to soils can affect microbial activity and thus the mineralization of soil organic carbon (SOC). Up to now, little is known about the processes leading to these priming effects and which fractions of organic matter (OM) are affected. The objectives of this study were to determine if SOC associated with isolated soil size fractions showed different susceptibility to priming effects, whether these pools are easily depleted, or whether the amount of substrate addition affects the extent of priming effects. In an incubation experiment, the effect of the uniformly ¹⁴C‐labeled substrates fructose and alanine on the mineralization of the SOC of a Bs horizon of a Haplic Podzol was investigated. The soil sample was fractionated into the three soil size fractions sand, silt, and clay by a mild sonication followed by sieving and sedimentation. Additionally, nonfractionated soil of the horizon was included in the experiment. Every soil sample received four substrate additions repeated at weekly intervals with 3.325 μg substrate‐C (mg SOC)^–1 and a final addition of 13.3 μg substrate‐C (mg SOC)^–1 after 4 weeks. The respiration was determined hourly and ¹⁴CO₂ was analyzed every 2, 4, and 7 d after the respective substrate addition. After 56 d, between 42% and 58% of the added substrates had been mineralized. Both substrates strongly increased the mineralization of the OM in all fractions (positive priming effects). The priming effects were always higher after the addition of the high substrate dose than during the first 4 weeks when four small doses were added. In general, the priming effects increased with decreasing particle size. Alanine generally caused higher priming effects than fructose in the soil size fractions (up to 280% vs. 231%, respectively). This indicates that alanine serves not only as an energy substrate but also as a N source and, thus, also promotes microbial growth. The strong priming effects in the silt and clay fraction (133% and 125% with fructose, 172% and 168% with alanine) showed, that not only the labile pool of OM is affected, but also a more stable pool characterized by higher ¹⁴C ages. We assume that the stability of the OM in these fractions is not only due to recalcitrance or to interactions with the minerals, but that it may also be caused by a substrate limitation of the degrading microorganisms.     

Effects of meliorative additives on the adsorption and binding forms of heavy metals in a contaminated topsoil from a former sewage farm

In a laboratory study, a heavy metal contaminated topsoil from a former sewage farm in Berlin was amended with different additives: lime, ash/gypsum, bark mulch, brown coal and combinations of these treatments. After 8 weeks of incubation, pH of the lime and ash/gypsum treatments increased to 6.2–6.3 compared to 5.2–5.3 in the control and the other treatments. Organic-C content rose from 42 g/kg in the control to 46–53 g/kg in the organic amendments. In reaction to the pH-increase the water soluble fraction of Cd, Cu and Zn was reduced by roughly 60%, 30% and 80% respectively. Cd- and Zn-binding forms as determined with NH₄-acetate- and EDTA-extracts were not affected by the treatments, while the ash/gypsum-treatment increased EDTA-extractable Pb by 17%. The exchangeable Cu-Fraction (NH₄-acetate extract) was reduced in all treatments to 82–93% of the control values, with the greatest effects in the tree bark amendment. The FREUNDLICH adsorption isotherms also show an increased sorption of heavy metals in the lime and ash/gypsum treatments. Organic amendments alone or in combination with lime had little effect on heavy metal adsorption.     

Zur Parametrisierung der Stickstoff-Mineralisierung in einem Ackerboden unter Feldbedingungen

A functional relationship for the nitrogen mineralization of an arable soil under field conditions In order to characterize the nitrogen mineralization of a poorly drained, loess-derived field soil (Aeric Fragiaqualf, loamy, mesic) a laboratory incubation experiment was carried out. The measured mineralization rate was expressed as a function of soil temperature and soil water content. At the same time, a field incubation experiment with buried soil samples (so-called Runge samples) was conducted. It was found that the laboratory incubation method overestimated the mineralization rate as compared with the field method. Accordingly, the laboratory data were adjusted. Additionally, it was found that management practices (fertilizer application, harvest, soil cultivation) influenced the course and the extent of the nitrogen mineralization.     

Einige Bemerkungen zur Bestimmung der Wasserleitfähigkeit mit der Bohrlochmethode

Some remarks concerning the determination of the hydraulic conductivity with the auger hole method Values of hydraulic conductivity, achieved with the auger hole method, may depend on the calculation procedure that is used. In this paper, values obtained with the method of Ernst (1950) are compared with such of Boast and Kirkham (1971). It is found, that differences of 25 percent and more may occur. It is concluded that care should be taken when conductivities are calculated from auger hole measurements. The method of Boast and Kirkham (1971) appears to be superior.     

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.     

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.