Regulation of urea synthesis in sublobular regions of the liver lobule by oxygen

Periportal and pericentral regions of the liver lobule were isolated from perfused rat liver using a micropunch and incubated in Krebs-Henseleit buffer (pH 7.6) containing 2% poly(ethylene glycol) in Eagle's basal medium, PMSF (50 micrograms/ml) and leupeptin (20 micrograms/ml) for 2 h at 25 degrees C under and O2/CO2 (95:5%) gas phase. Maximal rates of urea production from ammonium chloride were 96.4 +/- 8.7 and 32.8 +/- 5.4 mumol/g per h at 800 and 200 microM O2. Thus, urea synthesis was 2-3-times greater at high than low O2 tension in plugs from periportal and pericentral regions of the liver lobule.     

Effect of aflatoxin B1 on chromatin-bound ribonucleic acid polymerase and nucleic acid and protein synthesis in germinating maize seeds.

The treatment of germinating maize seeds (cv. Ganga 2) with aflatoxin B1 resulted in suppression of ribonucleic acid (RNA), protein, and deoxyribonucleic acid (DNA) synthesis at 3, 4, and 5 h, respectively. At or below the concentrations inhibitory for these in vivo syntheses, the toxin inhibited chromatin-bound DNA-dependent RNA polymerase activity. The synthesis of both polyadenylated and non-polyadenylated RNA was inhibited, but the effect on the former was more pronounced. Equilibrium dialysis and difference spectral and viscometric analyses showed a binding of aflatoxin B1 to DNA isolated from the seeds. It is proposed that the inhibition of RNA synthesis in maize seeds by the toxin is due to the interference with the RNA polymerase activity, which seems, at least partially, due to the impairment of DNA template functions.     

Avian Retrovirus pp32 DNA-Binding Protein I. Recognition of Specific Sequences on Retrovirus DNA Terminal Repeats

The avian retrovirus pp32 protein possesses a DNA-nicking activity which prefers supercoiled DNA as substrate. We have investigated the binding of pp32 to avian retrovirus long terminal repeat (LTR) DNA present in both supercoiled and linear forms. The cloned viral DNA was derived from unintegrated Schmidt-Ruppin A (SRA) DNA. A subclone of the viral DNA in pBR322 (termed pPvuII-DG) contains some src sequences, tandem copies of LTR sequences, and partial gag sequences in the order src-U(3) U(5):U(3) U(5)-gag. Binding of pp32 to supercoiled pPvuII-DG DNA followed by digestion of this complex with a multicut restriction enzyme (28 fragments total) permitted pp32 to preferentially retain on nitrocellulose filters two viral DNA fragments containing only LTR DNA sequences. In addition, pp32 also preferentially retained four plasmid DNA fragments containing either potential promoters or Tn3 "left-end" inverted repeat sequences. Mapping of the pp32 binding sites on viral LTR DNA was accomplished by using the DNase I footprinting technique. The pp32 protein, but not the avian retrovirus alphabeta DNA polymerase, is able to form a unique protein-DNA complex with selected regions of either SRA or Prague A LTR DNAs. Partial DNase I digestion of a 275-base pair SRA DNA fragment complexed with pp32 gives upon electrophoresis in denaturing gels a unique ladder pattern, with regions of diminished DNase I susceptibility from 6 to 10 nucleotides in length, in comparison with control digests in the absence of protein. The binding of pp32 to this fragment also yields enhanced DNase I-susceptible sites that are spaced between the areas protected from DNase I digestion. The protected region of this unique complex was a stretch of 170 +/- 10 nucleotides that encompasses the presumed viral promoter site in U(3), which is adjacent to the src region, extends through U(5), and proceeds past the joint into U(3) for about 34 base pairs. No specific protection or DNase I enhancement by pp32 was observed in experiments with a 435-base pair SRA DNA fragment derived from a part of U(3) and the adjacent src region or a 55-base pair DNA fragment derived from another part of U(3). The DNA sequence of Prague A DNA at the fused LTRs differs from that of SRA DNA. The alteration in the sequence at the juncture of the LTRs prevented pp32 from forming a stable complex in this region of the LTR. Our results are relevant to two aspects of the interaction between pp32 and LTR DNA. First, the pp32 protein in the presence of selected viral DNA restriction fragments possibly forms a higher order oligomer analogous to Escherichia coli DNA gyrase-DNA complexes or eucaryotic nucleosome structures. Second, the specificity of the binding suggests a role for pp32 and the protected DNA sequences in the retrovirus life cycle. The preferred sequences to which pp32 binds include two adjacent 15-base pair inverted terminal repeats at the joint between U(5) and U(3) in SRA DNA. This region is involved in circularization of linear DNA and is perhaps the site that directs integration into cellular DNA.     

Genetic heterogeneity within individual bovine rotavirus isolates

The genomic RNA patterns of six different bovine rotavirus isolates were analyzed on high-percentage polyacrylamide gels (12.5, 13.6, and 17.5%). In contrast to the RNA patterns exhibited by conventional gel systems, those on the high-percentage gels showed an improvement in segment resolution which consequently aided in the detection of extensive band splitting in these patterns. The ability to clone out various electrophoretically distinct virus subpopulations from each of the six isolates provided an explanation for the band splitting detected by the high-resolution gels. The significance of the coexistence of genetically distinct rotavirus populations within a single host is discussed.     

Dissociation of intracellular lysosomal rupture from the cell death caused by silica

The relationship between intracellular lysosomal rupture and cell death caused by silica was studied in P388d(1) macrophages. After 3 h of exposure to 150 μg silica in medium containing 1.8 mM Ca(2+), 60 percent of the cells were unable to exclude trypan blue. In the absence of extracellular Ca(2+), however, all of the cells remained viable. Phagocytosis of silica particles occurred to the same extent in the presence or absence of Ca(2+). The percentage of P388D(1) cells killed by silica depended on the dose and the concentration of Ca(2+) in the medium. Intracellular lyosomal rupture after exposure to silica was measured by acridine orange fluorescence or histochemical assay of horseradish peroxidase. With either assay, 60 percent of the cells exposed to 150 μg silica for 3 h in the presence of Ca(2+) showed intracellular lysosomal rupture, was not associated with measureable degradation of total DNA, RNA, protein, or phospholipids or accelerated turnover of exogenous horseradish peroxidase. Pretreatment with promethazine (20 μg/ml) protected 80 percent of P388D(1) macrophages against silica toxicity although lysosomal rupture occurred in 60-70 percent of the cells. Intracellular lysosomal rupture was prevented in 80 percent of the cells by pretreatment with indomethacin (5 x 10(-5)M), yet 40-50 percent of the cells died after 3 h of exposure to 150 μg silica in 1.8 mM extracellular Ca(2+). The calcium ionophore A23187 also caused intracellular lysosomal rupture in 90-98 percent of the cells treated for 1 h in either the presence or absence of extracellular Ca(2+). With the addition of 1.8 mM Ca(2+), 80 percent of the cells was killed after 3 h, whereas all of the cells remained viable in the absence of Ca(2+). These experiments suggest that intracellular lysosomal rupture is not causally related to the cell death cause by silica or {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187. Cell death is dependent on extracellular Ca(2+) and may be mediated by an influx of these ions across the plasma membrane permeability barrier damaged directly by exposure to these toxins.     

RNase E, an RNA processing enzyme from Escherichia coli.

An activity, RNase E, was purified about 100-fold from Escherichia coli cells, it can process p5 rRNA from a 9 S RNA molecule which accumulates in a mutant of E. coli defective in the maturation of 5 S rRNA. The enzyme requires Na+, K+, or NH4+, and Mg2+ or Mn2+. The molecular weight of the enzyme is about 70,000 and its pH optimum is 7.6 to 8.0. Its temperature optimum is around 30 degrees C, and it can be irreversibly inactivated at 50 degrees C. It has a very high degree of specificity but the reaction can be inhibited by nonspecific RNAs. We interpret its mode of action in producing p5 RNA as being accomplished in two steps, 9 S RNA is first processed to 7 S and 4 S, and subsequently 7 S is further processed to p5.     

Studies on the viscosity behavior of alkali halides in aqueous D-xylose solution

The viscosity behavior of ternary systems comprising sodium or potassium halides (concentration range 0.125–3M in aqueous D-xylose solution (0.4M at 25, 30, 35, and 40° has been determined. It is found that Moulik's equation holds for such concentrated solutions beyond the Einstein region. Furthermore, the “effective” rigid molar volume and the apparent B coefficient have been computed from the relative viscosity data by employing the Breslau-Miller treatment. The results are explained in terms of the structure-making or -breaking effects in solution by analyzing the values of the apparent B coefficient obtained for different temperatures.     

Intracellular disposition of [3H]-cocaine, [3H]-norcocaine, [3H]-benzoylecgonine and [3H]-benzoylnorecgonine in the brain of rats

[³H]-cocaine, [³H]-norcocaine, [³H]-benzoylecgonine and [³H]-benzoylnorecgonine were administered i.c. in equi-potent pharmacologic doses and the intracellular disposition and metabolism of each drug determined. Norcocaine and cocaine rapidly entered and egressed from the brain so that 4.8–6.1% of the radioactivity present in brain at one minute was observed at 30 minutes. The highest levels of subcellular radioactivity were generally found in the microsomal plus supernatant, followed by the nuclear and shocked mitochondrial fractions. No apparent localization of the radioactivity occured in synaptic membranes. The brain/plasma (B/P) ratio curves for cocaine and norcocaine were similar; however, the norcocaine values were considerably higher at each time interval. Benzoylecgonine and benzoylnorecgonine had higher comparative B/P ratios than cocaine or norcocaine and persisted in brain for a longer period of time so that 0.6–2.1% of the radioactivity present in brain at 1 hour was detected at 24 hours. Cocaine and norcocaine were extensively metabolized to the benzoylmetabolites. Benzoylecgonine was metabolized to benzoylnorecgonine and benzoylnorecgonine was unmetabolized. The brain disposition data and B/P ratios agreed quite well with the overall pharmacologic action of cocaine and its metabolites.     

Laboratory evaluation of a carabid larva,Chlaenius bioculatus [Col.: Carabidae] as a predator of lepidopterous pests

Food preference as well as feeding efficiency studies of the carabid predator revealed that the grub of theChlaenius bioculatus Chaud preferred mostPolytella gloriosae F. larvae in both 2nd and 3rd instar.Tarache tropica Guénée was preferred least by the grub predator in both instar.T. tropica was found toxic and grubs of the predator died after consumption.

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Résumé Les préférences alimentaires, de même que l'efficacité prédatrice deChlaenius bioculatus Chaud, montrent que ce carabide prédateur préfère le plus les larves dePolytella gloriosae F. du 2^e et 3^e stade.Tarache tropica Guénée est le moins attaqué aux deux stades.T. tropica est toxique et les larves du prédateur meurent après sa consommation.