Attachment of fluorescent metal chelates to macromolecules using “bifunctional” chelating agents

The use of “bifunctional” chelating agents to covalently attach stable chelates of terbium and europium to human serum albumin results in products whose lanthanide fluorescence may be studied easily at micromolar concentrations with standard instrumentation. The lanthanide ions may be added specifically and quantitatively to the protein-bound chelating groups in 0.1 M citrate, pH 6.5. The use of these reagents should greatly reduce ambiguities in the determination of distances between sites on macromolecules by energy transfer measurements.     

Liposomes. Effect of temperature on their mode of action on single frog skeletal muscle fibers

Liposomes containing the fluorescent dye 6-carboxyfluorescein were made from dipalmitoyl phosphatidylcholine and stearylamine. At 4°C the liposomes are adsorbed on the fiber surface and when the temperature is raised to 21°C, their contents are transferred directly into the fibers at a linear rate. Liposomes had little effect on the time course of the maximal twitch tension.     

Selective inhibition of leukotriene C4 synthesis and natural killer activity by ethacrynic acid

We have investigated the role of arachidonic acid (AA) metabolism in natural killer (NK) cell activity. Human nonadherent (NA) peripheral blood lymphocytes were used as effector cells against 51Cr-labeled K562 target cells. Synthesis of leukotriene C4 (LTC4) is dependent on glutathione S-transferase (GST). We have chosen to study three putative GST inhibitors, namely, ethacrynic acid (ET), caffeic acid (CA), and ferulic acid (FA), with regard to NK activity and with regard to their effect on AA metabolism. The GST inhibitors inhibited NK lysis when added directly to the NK assay. The GST inhibitors inhibited LTC4 synthesis as induced by calcium ionophore A23187 in a dose-dependent manner similar to their inhibition of NK activity. However, only ET was selective, for it had little effect on LTB4, 5-hydroxyeicosatetraenoic acid, and prostaglandin E2 synthesis. LTC4 synthesis was associated with the NK-enriched fractions obtained from discontinuous Percoll gradients. NK-specific anti-Leu-11b antibody and C treatment could abrogate NK activity and LTC4 synthesis. ET was also inhibitory when NA cells were cultured at 37 degrees C for 18 hr. In this case, LTC4 could reverse the inhibitory effect of ET. Our data suggest that LTC4 plays an important role in NK activity.     

Kinetics of toluene degradation by a nitrate-reducing bacterium isolated from a groundwater aquifer

Groundwater from a xylene-contaminated acquifer was enriched in the laboratory in the presence of toluene, xylenes, ethylbenzene, and benzene. A pure culture that degrades toluene and m-xylene under nitrate-reducing conditions was isolated. Fatty acid analysis, 16S rRNA sequencing, and morphological traits indicate that the isolate was a strain of Azoarcus tolulyticus. The kinetics of toluene degradation under nitrate-reducing conditions by this isolate was determined. Nitrate reduction does not proceed beyond nitrite. Nitrate and toluene are substrate limiting at low concentrations, whereas toluene, nitrate, and nitrite are inhibitory at high concentrations. Several inhibition models were compared to experimental data to represent inhibition by these substrates. A kinetic model for toluene and nitrate degradation as well as for cell growth and nitrite production was developed and compared to experimental data. The results of this work may find important application in the remediation of groundwater aquifers contaminated with aromatic hydrocarbons. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 82-90, 1997.     

A CR1 element is embedded in a novel tandem repeat (HinfI repeat) within the chicken genome.

Highly repetitive DNA sequences constitute a significant portion of most eukaryotic genomes, raising questions about their evolutionary origins and amplification dynamics. In this study, a novel chicken repetitive DNA family, the HinfI repeat, was characterized. The basic repeating unit of this family displays a uniform length of 770 bp, which was defined by the recognition site of HinfI. The HinfI repeat was specifically localized in the pericentric region of chromosome 4 by fluorescence in situ hybridization and constitutes 0.51% of the chicken genome. Interestingly, a chicken repeat 1 (CR1) element has been identified within this basic repeating unit. Like other CR1 elements, this CR1 element also displays typical retrotransposition characteristics, including a highly conserved 3' region and a badly truncated 5' end. This direct evidence from sequence analysis, together with our Southern blot results, suggests that the HinfI repeat may originate from a unique region containing a retrotransposed CR1 element.     

Grooming decisions by damselflies, age-specific colonisation by water mites, and the probability of successful parasitism.

We examined whether host damselflies (Ischnura verticalis) in different stages of development were differentially susceptible to parasitism by larval water mites (Arrenurus pseudosuperior). We found that mites were successful in reaching the parasitic phase more often if they colonised hosts closer to emergence. Thus, we predicted that more mites should colonise damselflies closer to emergence and damselflies closer to emergence should spend more time defending against mites. We found that mites colonised damselflies closer to emergence in one of two experiments, but that damselflies in different stages of development did not differ in time spent defending against mites.