Migration of arsenic(III) during bacterial oxidation of arsenopyrite in chalcopyrite concentrate by Thiobacillus ferrooxidans

During bacterial oxidation of the arsenopyrite that contaminated a chalcopyrite concentrate, the bioextraction of arsenic from the concentrate was examined. A long-term constant As(III) concentration, representing a large portion of the total arsenic, occurred in the leaching medium. As(III) was not further oxidized, either under bioextraction conditions or by Fe(III) in the presence of the mesophilic bacterium Thiobacillus ferooxidans. These results are discussed in relation to the influence of leaching microorganisms on the form of arsenic in the solution. Dissolved As(III) could be reversed into a solid phase by adsorption of As(III) by forming an iron precipitate. Correspondence to: M. Mandl     

Effects of protein kinase C modulation on NMDA receptor mediated regulation of neurotransmitter enzyme and c-fos protein in cultured neurons

The role of protein kinase C (PKC) in N-methyl-d-aspartate (NMDA) receptor-mediated biochemical differentiation and c-fos protein expression was investigated in cultured cerebellar granule neurons. The biochemical differentiation of glutamatergic granule cells was studied in terms of the specific activity of phosphate-activated glutaminase, an enzyme important in the synthesis of the putative neurotransmitter pool of glutamate. When the partially depolarized cells were treated with NMDA for the last 1 to 3 days (between 2 and 5 days in vitro), it elevated the specific activity of glutaminase. In contrast, NMDA had little effect on the activity of aspartate aminotransferase or of lactate dehydrogenase. Treatment of 10-day old granule neurons with NMDA also resulted in a marked increase in the immunocytochemically measured expression of c-fos protein. The increases in both the activity of glutaminase and the steady state level of c-fos protein were specific to the activation of NMDA receptors, as they were completely blocked byd,l-2-amino-5-phosphonovaleric acid. The specific stimulation of NMDA receptors in PKC-depleted granule neurons or in the presence of reasonably specific PKC inhibitors also produced significant elevation in the activity of glutaminase and the expression of c-fos protein. These increases were similar in magnitude to those observed in the granule neurons of the respective control groups. Our findings demonstrate that PKC is not directly involved in the NMDA receptor-mediated signal transduction processes associated with biochemical differentiation and c-fos induction in cerebellar granule neurons.     

Secondary structure of the 3'-noncoding region of flavivirus genomes: comparative analysis of base pairing probabilities.

The prediction of the complete matrix of base pairing probabilities was applied to the 3'' noncoding region (NCR) of flavivirus genomes. This approach identifies not only well-defined secondary structure elements, but also regions of high structural flexibility. Flaviviruses, many of which are important human pathogens, have a common genomic organization, but exhibit a significant degree of RNA sequence diversity in the functionally important 3''-NCR. We demonstrate the presence of secondary structures shared by all flaviviruses, as well as structural features that are characteristic for groups of viruses within the genus reflecting the established classification scheme. The significance of most of the predicted structures is corroborated by compensatory mutations. The availability of infectious clones for several flaviviruses will allow the assessment of these structural elements in processes of the viral life cycle, such as replication and assembly.     

Changes of prostacyclin and thromboxane synthesis in the course of mouse liver perfusion. Stimulated thromboxane A2 synthesis of freshly prepared isolated mouse hepatocytes

The formation of prostacyclin and thromboxane A2 (measured as 6-keto PGF1 alpha and TXB2 by radioimmunoassay) was investigated during a 30 min perfusion of mouse liver in a recirculation system. After cannulation of the portal vein an immediate increase of de novo synthesis and secretion of PGI2 occurred followed by a sharp decrease. Increased PGI2 synthesis was also followed by a continuous increase of TXA2 synthesis and secretion reaching a maximum at the end of the 30 min perfusion. Elevated TXA2 synthesis was also shown in freshly isolated hepatocytes investigated in the course of a 20 min incubation period immediately after the perfusion. However, the elevated TXA2 formation was not observed when it was measured after a 120 min preincubation of the cells. Both PGI2 and TXA2 production could be provoked to a similar extent by the addition of arachidonate and A 23187 immediately after the perfusion or after a 120 min preincubation.     

The response of sweet corn to HF and SO2 under field conditions

“Marcorss” sweet corn plants grown in field plots were exposed continuously in open-top chambers for 32 days to ambient air, charcoal-filtered air or charcoal-filtered air containing HF (ca. 0.5 μgF m⁻³), SO₂ (ca. 235 μg m⁻³), or the two pollutants combined. Elliptical chlorotic leasions appeared after 23 days on leaves of plants exposed to SO₂/HF, and shortly thereafter on plants exposed to all other treatments. At harvest, the number of plants with lesions was significantly greater in chambers supplied with SO₂/HF than in chambers with SO₂, HF, or filtered air.

The different treatments had no effect on fresh or dry weights of leaves, husks, or tassels, height of plants, or number of kernels per ear. Exposure to SO₂/HF reduced the fresh and dry weights of stalks. There were fewer mature ears in the SO₂/HF and unfiltered air treatments than in the others. The reduction in yield from SO₂/HF was about the same as that ascribed to ambient photochemical oxidants in the unfiltered air treatment.

HF combined with SO₂ had no effect on accumulation of S as compared with SO₂ alone, but there was a striking reduction in accumulation of foliar F in plants exposed to SO₂/HF as compared with HF alone.     

The flavivirus envelope protein E: isolation of a soluble form from tick-borne encephalitis virus and its crystallization.

By the use of limited trypsin digestion of purified virions, we generated a membrane anchor-free and crystallizable form of the tick-borne encephalitis virus envelope glycoprotein E. It retained its reactivity with a panel of monoclonal antibodies, and only subtle structural differences from the native protein E were recognized. Treatment with the bifunctional cross-linker dimethylsuberimidate resulted in the formation of a dimer. Crystallization experiments yielded hexagonal rod-shaped crystals suitable for X-ray diffraction analysis.     

cAMP dependent inhibition of thromboxane A2, prostacyclin and PGF2α synthesis in mouse hepatocytes

The role of cAMP dependent regulation in thromboxane A₂, prostacyclin and PGF_2α synthesis (measured by radioimmunoassay) was investigated in isolated mouse hepatocytes and in microsomal membranes prepared from these cells. In isolated hepatocytes N⁶,O²-dibutyryl cAMP inhibited the formation of all the three derivatives, while calcium ionophore A 23187 stimulated their synthesis. Addition of the dissociated catalytic subunit of cAMP dependent protein kinase and ATP to microsomal membranes inhibited the production of TXA₂, PGI₂ and PGF_2α by about 50% and this inhibition was counteracted by the combined addition of heat stable inhibitor protein of cAMP dependent protein kinase. It is concluded that in parenchylmal liver cells cAMP dependent phosphorylation is directly involved in the inhibition of prostanoid synthesis.