Purification and characterization of the membrane (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B

The membrane (Na⁺ + Mg²⁺)-ATPase of Acholeplasma laidlawii B has been solubilized with a Brij-58/sodium deoxycholate mixture and purified by a combination of gel filtration and ion-exchange chromatography. The purified, partially delipidated ATPase has a specific activity of 195 μmol P_i/mg protein per h, which could be enhanced by 25% upon the addition of exogenous phospholipids. The kinetic properties of the purified enzyme are similar to those of the native membrane-bound enzyme, suggesting that it has not been substantially altered during the purification procedure. The enzyme is an assembly of five polypeptide species and its kinetic properties suggest that it is dissimilar to other known ATPases.     

Hepatic microsomal NADPH-cytochrome P-450 reductase from little skate, Raja erinacea. Comparison of thermolability and other molecular properties with a mammalian enzyme

Components of little skate (an elasmobranch) and rabbit hepatic microsomal cytochrome P-450 dependent monooxygenase systems were examined for differences which might explain the decreasing xenobiotic-metabolizing activity of little skate microsomes assayed at temperatures above 30 degrees C. The proportion of saturated fatty acids in microsomal lipids and the habitat temperature are both lower in skate as compared to rabbit, which is consistent with the known adaptive pattern. The more thermolabile enzyme of the skate system in microsomal preparations is NADPH-cytochrome P-450 reductase. The optimal assay temperature for purified skate reductase (30 degrees C) is 10 degrees C lower than that for the purified rabbit reductase. The purified skate reductase differs from rabbit reductase in monomeric molecular weight, in peptides produced by partial proteolysis, in immunochemical properties, but not in flavin content.     

Effect of harvest intensity and ground flora establishment on inorganic-N leaching from a Sitka spruce plantation in north Wales,UK

Inorganic-N concentrations in soil solution of whole tree harvest (WTH) and conventional fell (CF) plots were monitored for two years before felling and four years after felling. Concentrations in the mineral soil after felling were higher than in standing forest for up to 14 months in both felling treatments. In the WTH plots inorganic-N concentrations then dropped steadily until four years after felling they approached zero. In contrast, inorganic-N concentrations of the CF plots remained comparatively large. Inorganic-N was dominated by nitrate throughout the period of the study, and especially in the mineral horizons.Felling debris was not a source of inorganic-N, unless indirectly through release and mineralisation of soluble organic-N. Vegetation cover, biomass and N content were substantially greater in the WTH plots two to three years after felling, compared with the CF. Vegetation cover and brash cover (slash cover in N. America) were negatively correlated. There was also a negative correlation between inorganic-N concentration in soil water samplers and the vegetation cover within the collection area of, or a 1 m square surrounding, these samplers.Two factors are probably responsible for the reduction in inorganic-N concentrations after felling in the WTH — the rapid re-establishment of vegetation and the lack of a N source in felling debris. In the CF plots, brash prevents re-establishment of vegetation over wide areas for at least four years. However, brash is not directly a source of inorganic-N at this stage.     

Determination of mercury in human serum and packed blood cells by neutron activation analysis

A method is described for the determination of mercury in human blood serum and packed blood cells employing neutron activation analysis. Great attention was devoted to the collection and manipulation of the samples. The accuracy and precision of the method were tested by analyzing biological reference materials and by comparing the concentrations measured in a number of serum samples to those obtained by another, independent technique (cold vapor atomic absorption spectrometry) in the same samples. The article reports the levels measured in blood serum and packed blood cells samples from 15 adult volunteers, as well as the figures determined in a “second-generation” biological reference material (freeze-dried human serum), prepared and conditioned at the University of Ghent.     

INORGANIC CARBON TRANSPORT IN RELATION TO CULTURE AGE AND INORGANIC CARBON CONCENTRATION IN A HIGH-CALCIFYING STRAIN OF EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)1

The relationships among inorganic carbon transport, bicarbonate availability, intracellular pH, and culture age were investigated in high-calcifying cultures of Emiliania huxleyi (Lohmann) Hay & Mohler. Measurement of inorganic carbon transport by the silicone-oil centrifugation technique demonstrated that gadolinium, a potential Ca²⁺ channel inhibitor, blocked intracellular inorganic carbon uptake and photosynthetic ¹⁴CO₂₊ fixation in exponential-phase cells. In stationary-phase cells, the intracellular inorganic carbon concentration was unaffected by gadolinium. Gadolinium was also used to investigate the link between bicarbonate and Ca²⁺ transport in high-calcifying cells of E. huxleyi. Bicarbonate availability had significant and rapid effects on pH_i in exponential- but not in stationary-phase cells. 4′, 4′-Diisothiocyanostilbene-2,2′-disulfonic acid did not block bicarbonate uptake from the external medium by exponential-phase cells. Inorganic carbon utilization by exponential- and stationary-phase cells of Emiliania huxleyi was investigated using a pH drift technique in a closed system. Light-dependent alkalization of the medium by stationary-phase cells resulted in a final pH of 10.1 and was inhibited by dextran-bound sulphonamide, an inhibitor of external carbonic anhydrase. Exponential-phase cells did not generate a pH drift. Overall, the results suggest that for high-calcifying cultures of E. huxleyi the predominant pathway of inorganic carbon utilization differs in exponential and stationary phase cells of the same culture.     

Spatial distribution and seasonal changes in methylmercury concentrations in shallow lakes

The environmental factors governing the distribution and behaviour of total and methylmercury within mercury contaminated shallow lakes, associated with the River Yare, Norfolk, UK, have been assessed in situ through the use of sediment cores. These were analysed for microbial and chemical changes on both a temporal and spatial scale. The distribution of total mercury proved to be site dependent and related to the hydrology, sediment transport dynamics, the degree of sediment disturbance and distance from the contamination source. The core profiles revealed a subsurface peak in total mercury with maximum concentrations residing at depths of 12 and 36 cm, depending upon location, with enrichment extending down to depths in excess of 88 cm. This vertical distribution was deemed to reflect historical emission in the late 1960s and early 1970s rather than post depositional migration effects. The distribution of methylmercury was distinct from that of its inorganic counterpart since it also displayed temporal variability with highest concentrations occurring in the spring and summer. Maximum concentrations also prevailed in the uppermost 12 cm of sediment, with peak loadings at or just below the sediment/water interface and detectable levels being restricted to the upper 36 cm. The temporal and spatial behaviour of methylmercury appeared to reflect variations in redox potential, the availability of the Hg²⁺ ion and the nature of microbial populations.     

Seasonal variability in mercury inputs into the Ria de Aveiro,Portugal

Water, suspended particulate matter (SPM) and sediments were collected from the Esteiro de Estarreja (Ria de Aveiro, Portugal), which receives considerable quantities of waste mercury from a chlor-alkali plant. Dissolved and particulate Hg concentrations in the effluent ranged between 4 –167 g I^–1 and 141–3144 g g^–1, respectively, at pH values of >10. The effluent plume undergoes significant chemical changes during advection downestuary. The evidence suggested that adsorption of dissolved Hg onto organic-rich SPM was an important process. A maximum sediment Hg concentration of 500 g g^–1 was found about 1.5 km from the discharge, as a result of the settling of Hg-rich SPM. Downestuary Hg concentrations in sediments decline to about 100 g g^–1 at the mouth of the Esteiro. The particle-water interactions are discussed in terms of the transport of dissolved and particulate Hg into the Ria de Aveiro.     

Mercury (Hg2+) and zinc (Zn2+): Two divalent cations with different actions on voltage-activated calcium channel currents

Summary 1. We examined the actions of mercury (Hg²⁺) and zinc (Zn²⁺) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique.2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of –80 to 0 mV (mainly L- and N-currents) were reduced by Hg²⁺ and Zn²⁺. The threshold concentration for Hg²⁺ effects was 0.1 µM and that for Zn²⁺ was 10µM. Voltage-activated calcium channel currents were abolished (>80%) with 5µM Hg²⁺ or 200µM Zn²⁺. The peak calcium current was reduced to 50% (IC₅₀) by 1.1µM Hg²⁺ or 69µM Zn²⁺. While Zn²⁺ was much more effective in reducing the T-type calcium channel current—activated by jumping from –80 to –35 mV—Hg²⁺ showed some increased effectiveness in reducing this current.3. The effects of both cations occurred rapidly and a steady state was reached within 1–3 min. While the action of Zn²⁺ was not dependent on an open channel state, Hg²⁺ effects depended partially on channel activation.4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg²⁺ and with higher concentrations (>100µM) of Zn²⁺.5. As Zn²⁺ in the concentration range used had no influence on resting membrane currents, Hg²⁺ caused a clear inward current at concentrations µM.6. In the present study we discuss whether the actions of both metals on voltage-activated calcium channel currents are mediated through the same binding site and how they may be related to their neurotoxic effects.