Effect of breath-hold time on DLCO(SB) in patients with airway obstruction

The single-breath diffusing capacity of the lung for CO [DLCO(SB)] is considered a measure of the conductance of CO across the alveolar-capillary membrane and its binding with hemoglobin. Although incomplete mixing of inspired gas with alveolar gas could theoretically influence overall diffusion, conventional calculations of DLCO(SB) spuriously overestimate DLCO(SB) during short breath-holding periods when incomplete mixing of gas within the lung might have the greatest effect. Using the three-equation method to calculate DLCO(SB) which analytically accounts for changes in breath-hold time, we found that DLCO(SB) did not change with breath-hold time in control subjects but increased with increasing breath-hold time in both patients with asthma and patients with emphysema. The increase in DLCO(SB) with increasing breath-hold time correlated with the phase III slope of the single-breath N2 washout curve. We suggest that in patients with ventilation maldistribution, DLCO(SB) may be decreased for the shorter breath-hold maneuvers because overall diffusion is limited by the reduced transport of CO from the inspired gas through the alveolar gas prior to alveolar-capillary gas exchange.     

Effects of temperature and CO2 enrichment on kinetic properties of phospho-enol-pyruvate carboxylase in two ecotypes of Echinochloa crus-galli (L.) Beauv., a C4 weed grass species

Summary Two populations of Echinochloa crus-galli (Québec, Mississippi) were grown at the Duke University Phytotron under 2 thermoperiods (28°/22°C, 21°/15°C day/night) and 2 CO₂ regimes (350 and 675 l l^-1). Thermostability, energy of activation (E _a ),K _m (PEP), K _m (Mg⁺⁺), and specific activity of phospho-enol-pyruvate carboxylase (PEP_c) were analyzed in partially purified enzyme preparations of plants grown for 5 weeks. Thermostability of PEP_c from extracts (in vitro) and leaves (in situ) was significantly higher in Mississippi plants. In vitro denaturation was not appreciably modified by thermal acclimation but CO₂ enrichment elicited higher thermostability of PEP_c. In situ thermostability was significantly higher than that of in vitro assays and was higher in Mississippi plants acclimated at 28°/22°C and in plants of the two ecotypes grown at 675 l l^-1 CO₂. E _a (Q ₁₀ 30°/20°C) for PEP_c was significantly lower in Québec plants as compared to Mississippi and no acclimatory shifts were observed. Significantly higher K _m's (PEP) in 20°C assays were obtained for Mississippi as compared to Québec plants but values were similar at 30°C and 40°C assays. K _m (Mg⁺⁺) decreased at higher assay temperatures and were significantly lower for PEP_c of the Québec ecotype. No significant changes in K _m (Mg⁺⁺) values were associated with modifications in temperature on CO₂ regimes. PEP_c activity measured at 30°C was significantly higher for Québec plants when measured on a leaf fresh weight, leaf area or protein basis but not on a chlorophyll basis. Significantly higher PEP_c activity for both genotypes was observed for plants acclimated at 21°/15°C or grown at 675 l l^-1 CO₂. Net photosynthesis (Ps) and net assimilation rates (NAR) were higher in Québec plants and were enhanced by CO₂ enrichment. NAR was higher in plants acclimated at low temperature, while an opposite trend was observed for Ps. PEP_c activities were always in excess of the amounts required to support observed rates of CO₂ assimilation.     

Distichia acicularis sp. nov. – a new cushion forming Juncaceae from the high Andes of Ecuador

Distichia acicularis is described as a new species of Juncaceae. It occurs in the high Andes of Ecuador between 3200 m and 4200 m above sea level. Its closest relative is D. muscoides Nees & Meyen from which it is distinct through its narrow, linear, mucronate leafblades and its 1–3 mm long auricles at the junction of the leafsheath to the blade.     

The immunocytochemical demonstration of Toxoplasma antigen in the brains of congenitally infected mice

The peroxidase anti-peroxidase immunocytochemical staining method was used to identify Toxoplasma antigen in paraffin embedded sections of the brains of 22 mice congenitally infected with the parasite. Intact Toxoplasma tissue cysts were readily demonstrated in the brain in all cases. In 4 of the 22 infected mice there was evidence of rupture of the cyst wall and/or presence of extra-cystic Toxoplasma antigen. Further support for the extra-cystic location of Toxoplasma antigen was obtained by electron microscopy of reprocessed tissue which revealed endozoites in the area immediately surrounding a ruptured cyst. The possible implications of these findings in relation to the pathogenesis of congenital toxoplasmic meningo-encephalitis are discussed.     

Cloning in Streptococcus lactis of plasmid-mediated UV resistance and effect on prophage stability

Plasmid pIL7 (33 kilobases) from Streptococcus lactis enhances UV resistance and prophage stability. A 5.4-kilobase pIL7 fragment carrying genes coding for both characters was cloned into S. lactis, using plasmid pHV1301 as the cloning vector. The recombinant plasmid was subsequently transferred to three other S. lactis strains by transformation or protoplast fusion. Cloned genes were expressed in all tested strains.     

Phytoplankton population dynamics of a small reservoir: physical/biological coupling and the time scales of community change

This paper describes the day-to-day changes in species compositionthat resulted from intermittent wind mixing of the surface watersof a small reservoir. Two major scales of community change weredetected: a short-term (>1 day) scale associated with theredistribution of cells within the basin, and a 5–14-dayscale associated with growth responses. The physical scalesof change were found to be almost identical to the biologicalscales: wind stress caused changes in the temperature gradientof surface waters at scales of a day, and major vertical mixingevents occurred at scales of 10–14 days. The presenceof buoyant species ensured that rapid advection of populationsfollowed wind events. Community change was a function of bothadvection and growth, so that both real and apparent changesin abundance occurred. The observed seasonal succession wasboth a true succession and a changing sequence of populationsdependent on horizontal advection of water within the basin.Consistent stratification was present throughout the summerperiod and phytoplankton diversity was low. Even so, the seasonalsuccession was best described as a series of allogenic perturbationsfollowed by biological restructuring of the community. Dailysampling was necessary to document fully the mechanisms drivingthe seasonal succession of species.     

Chromosome 8 breakpoint far 3'' of the c-myc oncogene in a Burkitt''s lymphoma 2;8 variant translocation is equivalent to the murine pvt-1 locus.

The 2;8 variant translocation of human Burkitt's lymphomas is closely related cytogenetically to the t(6;15) of murine plasmacytomas; both involve a reciprocal exchange between the Ig kappa locus and a band region indistinguishable from that bearing the c-myc oncogene. To define their molecular relationship, we have compared cloned chromosome 8 DNA from the t(2;8) breakpoint in the human Burkitt's lymphoma JBL2 with cloned DNA from the murine pvt-1 locus, the major chromosome 15 breakpoint region in murine t(6;15). DNA sequencing and Southern blot analysis shows that these two regions are homologous. Thus the t(2;8) in JBL2 is the molecular equivalent of many murine t(6;15). The murine pvt-1 locus lies an unknown distance 3' of c-myc; analysis of DNA from several tumours with c-myc amplification reveals that pvt-1 is co-amplified in at least one case, placing pvt-1 approximately 100-500 kb 3' of c-myc. The significance of these results with respect to the role of pvt-1 in tumorigenesis is discussed.     

Immobilization of lactate dehydrogenase on polyacrylamide beads

Pig muscle lactate dehydrogenase (L-lactate:NAD oxidoreductase, EC 1.1.1.27) was covalently immobilized on polyacrylamide beads containing carboxylic functional groups activated by water-soluble carbodiimide. The effects of immobilization on the catalytic properties and stability of the lactate dehydrogenase were studied. There was no shift in the pH optimum of the immobilized enzyme compared to that of the soluble one. The apparent optimum temperature of the soluble enzyme was 65 degrees C, while that of the immobilized enzyme was between 50 and 65 degrees C. The apparent Km values of the immobilized enzyme with pyruvate and NADH substrates were higher than those of the soluble enzyme. As a result of immobilization, enhanced stabilities were found against heat treatment, changes in pH, and urea denaturation.     

Molecular cloning of cDNA for rat L-type pyruvate kinase and aldolase B

Two double-stranded cDNA recombinant pBR322 plasmid libraries were constructed starting from high carbohydrate diet rat liver poly(A)+ mRNA, either fractionated by denaturing sucrose gradient centrifugation for the cloning of L-type pyruvate kinase cDNA, or nonfractionated for aldolase B. Both libraries were screened with single-stranded cDNA probes reverse transcribed from fasted or high carbohydrate diet rat liver mRNAs. mRNAs from fasted animals were also fractionated by sucrose gradient centrifugation and mRNAs from the fed animals were, in addition, further purified by high performance liquid gel filtration chromatography. Those clones hybridizing with the "positive" probe (from animals fed the high carbohydrate diet) and not with the "negative" one (from fasted animals) were preselected and their plasmid DNA was purified and analyzed by positive hybridization-selection. Thirty of 4500 bacteria colonies transformed by recombinant plasmids were preselected by differential screening for pyruvate kinase, and 8 of 864 colonies for aldolase B. Twenty-two recombinant plasmids for pyruvate kinase and two for aldolase B were shown to contain specific cDNA inserts by positive hybridization-selection. Plasmids DNAs of some pyruvate kinase and aldolase B clones (whose inserts ranged from 700 to 1050 bases in length) were labeled by nick translation and used as probes for Northern blot hybridization. The pyruvate kinase cDNA probes recognized mainly a 3400-base RNA species which was detected in high carbohydrate diet rat liver, but not in fasted rat liver and in tissues which do not synthesize L-type pyruvate kinase. In addition, some pyruvate kinase probes hybridized with minor RNA species of about 2000 bases in length, only observed after carbohydrate diet. For aldolase B, the recombinant plasmid DNA hybridized with a single RNA species of 1750 bases. This RNA, detected in kidney, small intestine and liver, was induced by a high carbohydrate diet and increased with liver development. The rat probe cross-hybridized with human aldolase B messenger RNA.