The Breathing Cell: Cyclic Intermembrane Distance Variation in Reverse Electrodialysis.

The breathing cell is a new concept design that operates a reverse electrodialysis stack by varying in time the intermembrane distance. Reverse electrodialysis is used to harvest salinity gradient energy; a rather unknown renewable energy source from controlled mixing of river water and seawater. Traditionally, both river water and seawater compartments have a fixed intermembrane distance. Especially the river water compartment thickness contributes to a large extent to the resistance of the stack due to its low conductivity. In our cyclic approach, two stages define the principle of the breathing concept; the initial stage, where both compartments (seawater and river water) have the same thickness and the compressed stage, where river water compartments are compressed by expanding the seawater compartments. This movement at a tunable frequency allows reducing stack resistance by decreasing the thickness of the river water compartment without increasing permanently the pumping losses. The breathing stacks clearly benefit from the lower resistance values and low pumping power required, obtaining high net power densities over a much broader flow rate range. The high frequency breathing stack (15 cycles/min) shows a maximum net power density of 1.3 W/m2. Although the maximum gross and net power density ever registered (2.9 W/m2 and 1.5 W/m2, respectively) is achieved for a fixed 120 µm intermembrane distance stack (without movement of the membranes), it is only obtained at a very narrow flow rate range due to the high pressure drops at small intermembrane distance. The breathing cell concept offers a unique feature, namely physical movement of the membranes, and thus the ability to adapt to the operational conditions and water quality.

Introduction of oxygen into the alkyl chain of N-decyl-dNM decreases lipophilicity and results in increased retention of glucose residues on N-linked oligosaccharides.

N-Alkylation of the alpha-glucosidase inhibitor 1-deoxynojirimycin (dNM) dramatically increases its inhibitory potency (Tan et al., J. Biol. Chem., 266, 14504-14510, 1991). However, the possibility of extending the alkyl chain to N-decyl-dNM is limited by an increase of detergent-like (amphiphilic) properties of long-chain alkylated dNM derivatives. Substitution of methylene groups in the N-decyl chain by oxygen reduced the amphiphilicity of N-decyl-dNM derivatives, while retaining their superior inhibitory properties. In intact HepG2 cells, the compound N-7-oxadecyl-dNM was found to result in the most pronounced retention of glucose residues on N-linked glycans. Permeabilization of the plasma membrane with the bacterial toxin Streptolysin O improves the inhibitory properties of the derivatives N-3,6,9-trioxadecyl-, N-7,10,13-trioxatetradecyl-, N-3-oxadecyl- and N-7-oxadecyl-dNM, but not those of dNM. These observations suggest differences in the mode of entry of the oxygen-substituted dNM derivatives in comparison with dNM. We observed that the dNM derivative N-3,6,9-trioxadecyl-dNM, devoid of inhibitory activity in intact cells, was inhibitory in Streptolysin O-permeabilized cells. Thus, the permeability barriers posed by plasma membrane and endoplasmic reticulum membrane are not equivalent. The use of a permeabilized cell system thus allows the elaboration of inhibitory principles for novel bioactive compounds where study of the isolated enzymes may not be possible, and where intact cells are not a suitable target due to permeability barriers.

Oncogene expression in Rauscher murine leukemia virus induced erythroid, myeloid and lymphoid cell lines.

A comparative study on the expression of nuclear and cytoplasmic oncogenes was carried out using the Northern blotting technique, in Rauscher virus induced primary leukemias and the more malignant transformed cell lines derived from them. The latter grow permanently in vitro. Hyperplastic spleens obtained from mice recovering from anemia were analysed as controls. In addition to the detection of mRNAs, Southern blotting was carried out to observe whether rearrangement or amplification of oncogenes had occurred. The results show that the nuclear oncogenes c-myc, c-myb and p53 are strongly expressed in leukemic tissue, whereas c-fos transcripts show a much weaker hybridization. The expression of two of these oncogenes, c-myc and c-myb was followed during differentiation in myeloid leukemic cells and showed a gradual decrease when compared with the actin gene, which is constitutively transcribed. A large number of cytoplasmic oncogenes is expressed in the leukemic cells lines, i.e. c-abl, c-fms, c-fes, c-src, c-ros, c-H-ras, c-K-ras and N-ras. Of these, transcripts coding for c-abl and c-src were absent in blast cells of acute erythroid leukemias. Transcripts coding for c-erb, c-mos and c-sis could also not be detected. A number of putative oncogenes which are reported to play a role in Moloney and Friend virus induced leukemias for instance pim-1, fis-1, fim-1 and fim-2 were also used for screening. Only expression of pim-1 in Rauscher virus induced myeloid leukemic cells and in primary acute erythroid leukemias could be observed. At the DNA level no rearrangement or amplification of any of the oncogenes investigated could be detected. The results show that a number of oncogenes are expressed simultaneously in the same leukemic tissue or cell lines. It therefore seems likely that the presence of transcripts of different oncogenes is associated with the progression of leukemia, but is not the primary cause of leukemogenesis or of the transformation of these cells into established cell lines.

Cloning of the genes involved in synthesis of coenzyme pyrrolo-quinoline-quinone from Acinetobacter calcoaceticus.

Mutants of Acinetobacter calcoaceticus LMD79.41 were isolated that are defective in the synthesis of the coenzyme pyrrolo-quinoline-quinone (PQQ). A gene bank of the wild-type. A. calcoaceticus genome was constructed with the binary plasmid system pLV21-RP4 delta Km. The DNA of A. calcoaceticus LMD79.41 was partially digested with Sau3A, and fragments of about 15 kilobases were inserted into the BamHI site of pLV21. The hybrid plasmids maintained in Escherichia coli were transferred by conjugation to the PQQ- mutants of A. calcoaceticus. One hybrid plasmid was isolated that complements all isolated PQQ- mutants. Subcloning of this plasmid in the vector pRK290 resulted in an insert of 5 kilobases on which at least four different genes involved in PQQ synthesis could be indicated. With Tn5 insertions the four PQQ genes were mapped, and it was shown that these genes are most probably located in three operons.