Rates of heat-induced pyrimidine alterations in synthetic polydeoxyribonucleotides

Hydrolytic damages to DNA can occur at physiological conditions. The possible role of DNA conformation on the distribution of such alterations of pyrimidines was investigated. Model compounds used were the synthetic alternating copolymer poly(dG-dC):poly(dG-dC) and the homopolymer poly(dG):poly(dC). Base damages were assayed by paper chromatography using polymers radioactively labeled in cytosine. Conformational changes were assayed by circular dichroic spectral changes. Incubation and heating of the polymers in 1 mM MnCl₂ caused the spectral shift reported for the left-handed Z-DNA conformation in the alternating copolymer and the change reported for the triple helix in the homopolymer. After incubation in 85°C, incidences of base damages were compared between the polymers. The presence of manganese reduced depyrimidination in both polymers. Rates of cytosine deamination to uracil were substantial and did not vary among the various conformational states.     

Helicases and RNA unwinding in translation: Current opinion in structural biology 1993, 3: 953–959

RNA helicases melt regions of duplex RNA in a process that requires energy derived from the hydrolysis of nucleoside triphosphates. The process of protein synthesis in prokaryotes and eukaryotes involves one proven RNA helicase (elF-4A) and several putative RNA helicases. Of these, one group of helicases is thought to unwind secondary structure in the 5′ non-coding region of mRNAs to facilitate ribosome binding. A second group is implicated in ribosome assembly, in particular in ribosomal RNA maturation.     

A mutant of Bacillus thuringiensis var. israelensis (B.t.i.) resistant to antibiotics

Summary PST, a spontaneous mutant of Bacillus thuringiensis var. israelensis (B.t.i.) resistant to penicillin, streptomycin and tetracycline was isolated by serial selections. In the absence of antibiotics it showed genetic stability for 16 generations. Mosquito larvicidal activity of PST was similar to that of B.t.i., its parental strain. It also maintained the specific antigenicity of B.t.i. although its rate of growth was somewhat lower, a generation time of 55 min for PST vs. 38 min for B.t.i. Cell concentration plays a major role in the phenomenon of PST resistance to penicillin.This antibiotic resistant mutant of b.t.i. provides us with an efficient tool to trace B.t.i. among the indigenous bacteria present in septic habitats in the field as well as inside the larval gut.     

Pressure, flow, and density relationships in airway models during constant-flow ventilation

Adequate CO2 elimination and normal arterial PCO2 levels can be maintained in dogs during apnea by delivering a continuous flow of inspired gas at high flow rate (1-3 l.min-1.kg-1) through tubes placed in the main-stem bronchi. However, during constant-flow ventilation (CFV) the mean alveolar pressure is increased, causing increased lung volume despite low pressures in the trachea. We hypothesized that the increased dynamic alveolar pressures during CFV were due to momentum transfer from the high-velocity jet stream to resident gas in the lung. To test this, we simulated CFV in straight tubes and in a branched airway model to determine whether changes in gas flow rate (V), gas density (rho), and tube diameter (D) altered the pressure difference (delta P) between alveoli and airway opening in a manner consistent with that predicted by conservation of momentum. Momentum analysis predicts that delta P should vary with V2, whereas measurements yielded a dependence of V1.69 in branched tubes and V1.9 in straight tubes. Substitution of heliox (80% He-20% O2) for air significantly reduced lung hyperinflation during CFV. As predicted by momentum transfer, delta P varied with rho 1.0. Momentum analysis also predicts that delta P should vary with D-2.0, whereas measurements indicated a dependence on D-2.02. The influence of V and rho on depth of penetration of the jet down the airway was explored in a straight tube model by varying the flow rate and gas used. The influence of geometry on penetration was measured by changing the ratio of jet-to-airway tube diameters.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fluorescent and Ferritin Labelling of Cuticle Surface Carbohydrates of Caenorhabditis elegans and Panagrellus redivivus

Caenorhabditis elegans and Panagrellus redivivus were investigated for surface carbohydrates using fluorescent-labelled and ferritin-labelled lectins. Rhodamine-labelled Concanavalin A was specifically located in the cephalic region of both species. Rhodamine-labelled wheat germ agglutinin was located over the entire cuticle of P. redivivus but was absent on C. elegans. Rhodamine-labelled peanut agglutinin and Limax flavus agglutinin did not label nematodes of either species. Galactose and sialic acid were not detected on either species, whereas mannose-glucose residues were specifically localized in the head areas of both species. No detectable N-acetylglucosamine occurred on C. elegans, but it was evenly distributed over the cuticle surface of P. redivivus.     

Oxyphenbutazone (Tandearil?) in Rhinoplasty—A Clinical Evaluation of Effectiveness

To evaluate the effectiveness of Oxyphenbutazone as an anti-inflammatory agent, a double-blind study of Oxyphenbutazone and a placebo in a group of 42 patients who had nasal cosmetic operations involving osteotomy was carried out. The observations included direct objective measurement of the width of the palpebral fissure after operation, grading of the severity of postoperative edema and ecchymosis from photographs, and observations by the patients regarding the clearing of the postoperative discoloration. It appeared from the results of these observations that Oxyphenbutazone is not effective in preventing postoperative edema in such operations or in promoting more rapid resolution of postoperative edema. It did appear to enhance the clearing of postoperative periorbital ecchymosis.     

Measurement of hydrogen peroxide in plasma and blood

Measurement of the oxygen metabolite hydrogen peroxide (H2O2) in biological fluids such as plasma could be of interest because it might indicate participation of toxic oxygen species in tissue injury. Recently several reports claimed to measure H2O2 using spectrophotometric and high pressure liquid chromatographic (HPLC) techniques that utilize oxidation of a substrate to a product by a peroxidase. In such a system it is crucial to perform two control experiments to verify whether the measured substance is H2O2. The specificity of the assay for H2O2 should be checked with catalase, and the degradation of H2O2 or inhibition of the assay system by the sample should be checked by determining the recovery of exogenously added H2O2. We performed both types of controls for HPLC and spectrophotometric determinations of H2O2 in plasma and blood. Our results indicate that contrary to previous reports in the literature the measured substance(s) in plasma or blood is not H2O2. Moreover, quantitative measurements of H2O2 in plasma or blood by HPLC was unreliable due to the irreversible binding of H2O2 to the column surface.     

Murine p53 inhibits the function but not the formation of SV40 T antigen hexamers and stimulates T antigen RNA helicase activity

We have characterized the effects of p53 on several biochemical activities of simian virus 40 (SV40) large tumor (T) antigen. While p53 induced a strong inhibition of the T antigen DNA helicase activity, surprisingly, its RNA helicase activity was stimulated. This supports the liklihood that the DNA and RNA helicase activities of T antigen reflect discrete functions. p53 did not significantly affect the ATP-dependent conversion of T antigen monomers to hexamers. However, the ability of these hexamers to assemble on a DNA fragment containing the viral origin was impaired by p53. Thus, these results suggest that p53 inhibits the function but not the formation of T antigen multimers. This conclusion was further supported by the observation that the addition of a purified p53:T antigen complex was as inhihitory as free p53 to the DNA helicase activity of free T antigen. Thus our data indicates that the targets of p53 inhibition are the functional units of T antigen, namely the hexamers.