PubMed · 8798191
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
S Doonan. 1996. Making and changing buffers.. https://doi.org/10.1385/0-89603-336-8%3A103
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Effects of temperature and ionic strength (S) on the local structure of tobacco mosaic virus RNA in phosphate buffer solution are studied by analyzing the small-angle X-ray scattering (SAXS) curves. The root-mean-square radius of a cross-section of RNA chain was kept at 0.845+/-0.005 nm over a wide range of S from 0.2 to 0.003 at 20 degrees C, whereas it gradually diminished from 0.85 to 0.61 nm when the temperature is raised from 20 to 50 degrees C at S = 0.2. Nevertheless, all of SAXS curves reflecting the backbone structures were equally mimicked by theoretical ones of freely hinged rod (FHR) models, i.e. several straight rods joined with freely hinged joints in the form of a combination of the letter Y, if the constituent rod lengths in the models are adjusted. From these facts, it is suggested that the local structure of the RNA chain in aqueous solution is characterized by an essential feature that unpaired bases in the partially double-stranded helix are constantly far isolated from each other along the helix and the rod-like structure of the helix is preserved over a range of helical contents. Such a characteristic local structure of the chain is entirely collapsed in the formamide solution at 50 degrees C.
Factors influencing the extent of formation of oxidizable reduction products in coulometric cells used for Karl Fischer (KF) determination of water were investigated. For methanolic KF reagents buffered with imidazole (Im) or diethanolamine (DEA) (separately or in combination), three parameters were found to be of outmost importance: the cathodic current density, the pH, and the concentration of protonated base (ImH+ or DEAH+). For reagents buffered with only Im, the relative formation of oxidizable reduction products varied in the range 2-40%; i.e., 51-70 micrograms of water was found for a 50 micrograms water sample, depending on the above-mentioned parameters. The lowest values were observed for reagents having a pH around 10 in combination with cathodic current densities in the range 2000-5000 mA cm-2. For all the Imbuffered reagents investigated, the addition of modifiers such as chloroform, hexanol, and carbon tetrachloride was found to decrease the formation of oxidizable reduction products significantly. For example, a reagent buffered at pH 10 containing 1 M hexanol gave less than 0.3% formation in the current density interval from 200 to 4000 mA cm-2. The best reagents based on the above-mentioned modifiers were tested in the continuous coulometric mode with errors typically in the interval 0-0.5% using optimum conditions. One prerequisite for obtaining such small errors with diaphragm-free continuous coulometry is to use a cathode area no larger than 0.002 cm2. For some of the reagents based on both Im and DEA, the formation of oxidizable reduction products was close to zero at certain current densities, although the analytical performance was not as good as for the reagents buffered solely by Im due to longer conditioning and titration times.
The reason for the selective vulnerability of motor neurons in amyotrophic lateral sclerosis (ALS) is primarily unknown. A possible factor is the expression by motor neurons of Ca(2+)-permeable AMPA/kainate channels, which may permit rapid Ca(2+) influx in response to synaptic receptor activation. However, other subpopulations of central neurons, most notably forebrain GABAergic interneurons, consistently express large numbers of these channels but do not degenerate in ALS. Indeed, when subjected to identical excitotoxic exposures, motor neurons were more susceptible than GABAergic neurons to AMPA/kainate receptor-mediated neurotoxicity. Microfluorimetric studies were performed to examine the basis for the difference in vulnerability. First, AMPA or kainate exposures appeared to trigger substantial mitochondrial Ca(2+) loading in motor neurons, as indicated by a sharp increase in intracellular Ca(2+) after addition of the mitochondrial uncoupler carbonyl cyanide p-(trifluoromethoxy)phenyl hydrazone (FCCP) after the agonist exposure. The same exposures caused little mitochondrial Ca(2+) accumulation in GABAergic cortical neurons. Subsequent experiments examined other measures of mitochondrial function to compare sequelae of AMPA/kainate receptor activation between these populations. Brief exposure to either AMPA or kainate caused mitochondrial depolarization, assessed using tetramethylrhodamine ethylester, and reactive oxygen species (ROS) generation, assessed using hydroethidine, in motor neurons. However, these effects were only seen in the GABAergic neurons after exposure to the nondesensitizing AMPA receptor agonist kainate. Finally, addition of either antioxidants or toxins (FCCP or CN(-)) that block mitochondrial Ca(2+) uptake attenuated AMPA/kainate receptor-mediated motor neuron injury, suggesting that the mitochondrial Ca(2+) uptake and consequent ROS generation are central to the injury process.