Effect of polymyxin B on the structure and the stability of lipid layers

Summary Polymyxin B (PX) does not penetrate phospholipid monolayers and bilayers at low field strength across the lipid layers. The degree of penetration of PX is evaluated from its effect on the capacitance of the monolayers and on the conductance of the bilayers. PX added to one side of a bilayer causes its destabilization, it also enhances destabilization of lipid monolayers at positive electric fields across the surface layer in the direction of the adsorbed PX. PX lowers very little the fluorescence polarization of 1,6-diphenyl 1,3,5 hexatriene embedded in phospholipid vesicles. It is suggested that the penetration mechanism of PX into gram-negative bacteria is based on transient local breakdown of the plasma membrane.     

Differential scanning calorimetry and enzymic activity of rat liver microsomes in the presence and absence of Δ1-tetrahydrocannabinol

The thermal transitions of rat liver microsomes and isolated lipids were investigated by using differential scanning calorimetry. Endothermic transitions at ≈?5°C and between ≈18° and 40°C were detected in the membranes and at ≈?10°C and between ≈10° and 20°C in the extracted lipids.Interaction with $\text{Δ}{}^1\text{-}\text{tetrahydrocannabinol}$ of microsomal membranes and of extracted lipids influences the thermotrophic behaviour as revealed by differential scanning calorimetry and eliminates the break in the Arrhenius plot of the enzymic activity of $\text{O-}\text{demethylase}$.     

Adult thymectomy promotes the manifestation of autoreactive lymphocytes.

Spleen cells from adult thymectomized mice (ATX) were assayed in a syngeneic graft vs host (GVH) model based upon enlargement of the draining popliteal lymph node following syngeneic cell inoculation into the hind footpad. Spleen cells from ATX mice have been found to induce a significantly higher increase in the weight of the regional lymph node than that induced by the injection of normal spleen cells. Irradiated spleen cells from ATX donors did not cause a similar increase, suggesting either that proliferation of the transferred cells was required at some stage of the reaction or that autoreactive cells are radiosensitive. Autoreactive cells were found in the spleen of mice 2 to 3 months after the thymectomy but were never found in the lymph nodes of such animals or in the thymus of intact mice. They are not phagocytic adherent cells and are not retained on nylon wool columns, which suggests that they belong to the T-cell lineage. Autoreactivity is lost when spleen cells from ATX donors are depleted of autologous rosette-forming cells (A-RFC) by centrifugation on a Ficoll-Hypaque gradient after rosette formation. Autoreactive spleen lymphocytes might belong to the population of A-RFC previously characterized as a population of immature T cells.     

CD3 negative "small agranular lymphocytes" are natural killer cells

We describe here that CD3-, CD16+ and/or CD56+ small lymphocytes, in a highly reproducible fashion, mediate a significant level of K562 killing that is, on a "per cell" basis, comparable to the cytolytic activity of CD3- LGL. The CD3- small lymphocytes appeared to have no granules based on light and electron microscopy and lack of right-angle scatter on the FACS; we thus refer to them as small "agranular" lymphocytes (SAL). The lytic activity against K562 is inhibited by treatment with either L-leucine methyl ester or EGTA, which are reported to effect granule-dependent killing. We suggest that the SAL have lytic molecules in their cytoplasm (which are sensitive to these treatments) but that these molecules are not organized into discrete granules as found in LGL. The CD3- SAL are phenotypically very similar to LGL and both SAL and LGL mediated equal and reproducible antibody-dependent cell-mediated cytotoxicity. These observations force redefinition of the concept of NK cells to include both CD3- LGL and CD3- SAL.     

Transfer RNA genes from Dictyostelium discoideum are frequently associated with repetitive elements and contain consensus boxes in their 5' and 3'-flanking regions.

A total of 68 different tRNA genes from the cellular slime mold Dictyostelium discoideum have been isolated and characterized. Although these tRNA genes show features common to typical nuclear tRNA genes from other organisms, several unique characteristics are apparent: (1) the 5'-proximal flanking region is very similar for most of the tRNA genes; (2) more than 80% of the tRNA genes contain an "ex-B motif" within their 3'-flanking region, which strongly resembles characteristics of the consensus sequence of a T-stem/T-loop region (B-box) of a tRNA gene; (3) probably more than 50% of the tRNA genes in certain D. discoideum strains are associated with a retrotransposon, termed DRE (Dictyostelium repetitive element), or with a transposon, termed Tdd-3 (Transposon Dictyostelium discoideum). DRE always occurs 50 (+/- 3) nucleotides upstream and Tdd-3 always occurs 100 (+/- 20) nucleotides downstream from the tRNA gene. D. discoideum tRNA genes are organized in multicopy gene families consisting of 5 to 20 individual genes. Members of a particular gene family are identical within the mature tRNA coding region while flanking sequences are idiosyncratic.     

Metabolic heterogeneity of isolated cortical and juxtamedullary glomeruli in adriamycin nephrotoxicity.

The anticancer drug adriamycin (ADR) is selectively toxic to glomerular cells when administered intravenously (5 mg/kg b.w.) to female MWF/Ztm rats. Recent data have shown that the proteinuria associated with the lesion does not occur in cortical glomeruli, suggesting the selective injury of juxtamedullary glomeruli. In the present study, the effect of ADR on glomerular metabolism was studied with special reference to possible differences between cortical and juxtamedullary glomeruli. On day 7 after ADR treatment, cortical and juxtamedullary glomeruli were separately isolated by the sieving method and 14C glucose oxidation to 14CO2 and the incorporation of 3H proline into macromolecules were measured in vitro and used to study target selective injury in ADR-treated rats compared to control rats. The investigations revealed differences in the response of cortical and juxtamedullary glomeruli to ADR. ADR treatment increased proline incorporation over a 4-hour incubation period in both glomerular populations compared to controls, but the effect was significantly (p less than 0.05) more pronounced in juxtamedullary glomeruli (juxtamedullary: 187 +/- 8% of control; cortical: 167 +/- 4% of control). Glucose oxidation was enhanced after 4 h only in juxtamedullary glomeruli (juxtamedullary: 132 +/- 3% of control; cortical: 82 +/- 10% of control). These data show that glomerular damage caused by ADR is associated with a stimulating effect on glomerular metabolism which is more marked in juxtamedullary than in cortical glomeruli, thus indicating a heterogenous response of different glomerular populations and supporting the concept that the selective damage of juxtamedullary glomeruli accounts for the proteinuria.     

Non-light-dependent Shikimate Pathway in Plastids from Pea Roots

Non-green plastids (leucoplasts) isolated from pea roots are shown to be considerably active in forming aromatic amino acids by the shikimate pathway which, in contrast to the chloroplast pathway, is independent of light. Supply of phosphoenolpyruvate and 3-dehydroquinate, 3-dehydroshikimate, shikimate and quinate effectively enhances the formation of aromatic amino acids suggesting an intra- or/and intercellular intermediate transport.     

Nucleotide sequence and phylogenetic implication of the ATPase subunits β and ε encoded in the chloroplast genome of the brown alga Dictyota dichotoma

We have cloned and sequenced the genes atpB and atpE, coding for CF₁ subunits and , respectively, of the chloroplast genome of the brown alga Dictyota dichotoma. Although the coding site of atpE cannot be demonstrated by heterologous Southern hybridizations, a 417 bp reading frame 3 to atpB was identified as the gene atpE by sequence similarities with atpE genes from other sources. A maximum sequence identity of 30% is found between the predicted amino acid sequence of the Dictyota subunit and the corresponding cyanobacterial subunits. Including conserved amino acid replacements, the Dictyota subunit exhibits about 70% sequence similarity with the cyanobacterial and land plant subunits. As in cyanobacteria, the atpE gene does not overlap the preceding gene atpB. The deduced amino acid sequence of atpB is 74–79% identical to the corresponding cyanobacterial and chloroplast subunits. Entirely conserved are regions referred to as the catalytic and/or regulatory sites of ATP formation, including interacting regions between subunits and . A phylogram predicted from F₁/CF₁- subunits of eleven different organisms suggests a common evolutionary origin of plastids from chlorophytes and brown algae.     

Sequences of DNA fragments contacting the nuclear lamina in vivo.

To study the DNA sequences contacting the nuclear lamina (NL) in vivo, Ehrlich ascites tumor cells were UV-irradiated. The NL was purified, and the DNA fragments covalently linked to the lamina proteins in vivo were cloned and sequenced. Although heterogeneous in length and composition, the sequences displayed homology to the introns and/or flanking regions of different genes, suggesting that functionally distinct regions are organized in a topologically defined manner at the nuclear periphery.