Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary When ultraviolet irradiation of doubly auxotrophic conidia was preceded or followed by weakly mutagenic doses of DEB, the frequency of adenine-reversions was increased above additivity, while that of inositol-reversions was additive or—usually—was decreased below additivity. These interactions did not affect completed revertants nor were they due to plating interactions between potential revertants and the non-mutant background cells. The interaction was stronger when DEB was given as pretreatment than when it was given as post-treatment. During the DEB-treatment, sensitivity to interaction increased from the low effect observed with post-treatment to the higher one typical for pretreatment. Irradiation towards the end of the treatment period gave the same interaction as irradiation of treated and washed cells. In post-treatment experiments, the irradiated cells retained their capacity for interaction with DEB undiminished for at least on hour. In pretreatment experiments, the washed cells retained their capacity for interaction with UV over at least 16 minutes. After 2 hours, interaction was diminished; after 4 hours, it had disappeared. These results suggest a number of conclusions. (a) Interaction is mainly or wholly due to the effect of DEB on UV-induced mutations. (b) Interaction does not occur at the level of the primary lesions in DNA but at some later step in mutagenesis. (c) The mechanism of interaction is not the same for the two types of reversion. (d) The enhanced frequency of adenine-reversions is possibly due to inhibition of a repair enzyme by DEB. (e) The decreased frequency of inositol-reversions does not appear to be due to inositol-less death, but does seem connected with some specific phenotypic feature of inositol-reversions.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 109 (1970), S. 285-291 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Weak doses of DEB given before or after a moderately high dose act as “booster” for the production of adenine-reversions. Fractionation of a moderate or high dose into a succession of weak ones yields a dose-effect curve that lies above the linear curve expected for additivity of the fractions but below that found after continuous exposure. The results lend support to the view that DEB, in addition to producing potential adenine-reversions in DNA, promotes their realization by its effect on some cellular process or processes, and that this is the cause of the steep dose-response to continuous exposure.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the strain ad 3A 38701 inos 37401, UV usually produces about twice as many inositol-as adenine-reversions. We have shown previously that this inositol-specificity of UV can be reversed into adenine-specificity by pre- or post-treatment with low doses of the adenine-specific DEB. We now have tested two more adenine-specific mutagens, nitrous acid (NA) and a mixture of hydrogen peroxide and formaldehyde (HF) and one inositolspecific mutagen nitrosoethylurethane (NEU) for interaction with UV. The former two substances behaved like DEB in reversing the inositol-specificity of UV when given as pre-or post-treatment. Pre-treatment with NEU always enhanced the frequency of inositol-reversions beyond additivity. At low doses, it also enhanced the frequency of adenine-reversions. The results are discussed in relation to mutagen specificity. They indicate that specificity may arise from the effects of treatment on cellular events in any one of the three major parts of the mutational pathway: repair, expression, growth of completed mutants into clones.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1573-7373
    Keywords: clear cell sarcoma ; renal neoplasms ; brain metastasis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We describe a 5 year old boy with a 5.5 cm right frontal lobe brain metastasis from primary clear cell sarcoma of the kidney without evidence of tumor-associated edema or contrast enhancement on either computed tomography or magnetic resonance imaging. The metastasis regressed but did not disappear with chemotherapy and dexamethasone, and the residual tumor was removed surgically. On histological examination the majority of the tumor was composed of mature connective tissue with a rim of typical renal clear cell sarcoma cells at the brain-tumor interface. The avascular and desmoplastic nature of the metastasis may explain the unusual radiographic features. Brain metastases from this tumor have only infrequently been reported; therefore a brief review of this rare tumor is provided.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 74 (1952), S. 2828-2832 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 103 (1968), S. 72-104 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Dose-response curves to seven mutagens (X, UV, NEU, NMU, NA, HF, DEB) have been determined for a diauxotrophic strain of Neurospora (38701 ad-3A, 37401 inos). The data have been discussed from two points of view: mutagen specificity, and the meaning of dose-response curves in mutation research. The main results are as follows. 1. If mutagen specificity is defined as an overall excess of one type of reversion over the other, then three mutagens (UV, NEU, NMU) are specific for the inositol-allele, and four mutagens (X, HF, NA, DEB) are specific for the adenine-allele. 2. For all mutagens, the degree of specificity is dose-dependent, for some of them (HF, NA, DEB) strongly so. This is due to the fact that in every case the two dose-response curves either converge (X) or diverge (UV, NEU, NA, HF, DEB): after NMU treatment, they first diverge and, at still higher doses, converge again. As a result, an excess of one reversion type at low doses becomes reduced (X) or amplified (UV, NEU, NA, HF, DEB) at higher doses or reaches a maximum at an intermediate dose (NMU). These observations make it imperative to assess degrees of mutagen specificity from a comparison between dose-response curves and not from the ratio of the two reversion types at an arbitrarily chosen dose. 3. X and HF (which probably resembles X in its mode of action) are the only mutagens that show marked specificity already at the lowest doses. We have interpreted this to mean that the X-ray “target”, i.e. the probability that a random hit anywhere in the genome will cause a reversion, is at least ten times as large for the adenine-allele as for the inositol-allele. This agrees roughly with the ratio between the spontaneous reversion frequencies. 4. For all other mutagens, specificity is greatly reduced or altogether abolished at the lowest doses. Even DEB, which at high doses may produce several hundred times as many adenine- as inositol-reversions, produces only a few times as many at very low doses or when given to a growing culture instead of to a suspension of conidia. We have interpreted this to mean that the two alleles offer the same or a very similar “target” to every one of these five mutagens. The specificities observed at higher doses do not, therefore, arise from specific reactions between mutagen and DNA but from specific treatment effects on later steps in the mutation process, e.g. repair or enzyme function. This conclusion is supported by the fact that mutagen specificity can be modified by genetic background or by experimental conditions before, during or after treatment. The practical significance of this conclusion lies in the possibility that some direction may be given to the mutation process without having to await the — very improbable — discovery of chemicals with specific effects on individual genes. 5. The kinetics of mutation induction varied between mutagens; they rarely were the same for the two reversion types and could be modified by experimental conditions. The curves relating reversion frequency to dose varied from less than linear to more than quadratic. In most experiments, the dose exponent was higher for the more frequent reversion type than for the less frequent one. Reasons are given for considering the dose-response curves as composite ones in which the one-hit kinetics of the primary reaction between mutagen and DNA is overlaid by the kinetics of treatment effects on cellular conditions relevant to the mutation process. The strong exponential component (e c·dose) found in some of the dose-response curves suggests, but does not prove, that exponential inactivation of a repair enzyme may be one of these components.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The symmetric and antisymmetric stretch spectra of a˜ 1A1 CH2 are measured with Doppler-limited resolution by infrared flash-kinetic spectroscopy between 2600 and 3050 cm−1. The spectra are significantly perturbed by spin–orbit interactions between near-resonant levels of X˜ 3B1 in both lower and upper levels of the transitions, and by Coriolis interaction between symmetric and antisymmetric stretch states. The triplet character of the perturbed levels is detected by observing broadening of MJ structure in a magnetic field of about 1 kG. The levels that are likely to be perturbed by triplet methylene are identified using the experimentally observed and theoretically calculated 3B1 energy level structure. The term values of the remaining symmetric and antisymmetric stretch levels are simultaneously fit to Watson's Hamiltonian including Coriolis coupling. This analysis provides the remaining information needed to determine the equilibrium rotational constants [Ae =19.8054(206), Be=11.2489(45), and Ce =7.2386(36) cm−1 ], and, therefore, the equilibrium structure (re=1.107 A(ring), and θe =102.4°) of this fundamentally important carbene. The experimental and theoretical structures are in good agreement.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The scattered intensity function S(q, c) and the intermediate scattering function S(q, c, τ) of poly-(α-methyl styrene) (Mω = 5.71 × 105, 1.17 × 106, and 2.96 × 106) in toluene in the dilute concentration region were measured as functions of concentration and scattering vector q. In infinitely dilute solution, the intensity function S(q, 0) agrees well with the Debye function for u 〈 7, where u is (qRg)2. At finite concentration S(q, c) varies from its thermodynamic value at low u to the single chain value at high u. Theoretical calculations of S(q, c) are in quantitative agreement with the observed scattering function in very dilute solutions. The intermediate scattering function S(q, c, τ) is a single exponential decay with decay rate Dmq2 for u ≪ 1. For u 〉 1, S(q, c, τ) is nonexponential, and when analyzed with a discrete inversion method, yields a bimodal distribution of decay rates. Both components are well represented as single exponential decays. D0 can be obtained from the slower component. The decay rate of the faster component is a continuous function of u and approaches q2 dependence at high u.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 0887-6266
    Keywords: light scattering ; glass transition ; distributions of relaxation times ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Slow relaxing longitudinal density fluctuations in bulk syndiotactic poly (n-butyl methacrylate) [PBMA] were studied by photon correlation spectroscopy as a function of temperature from 70 to 90°C. The shape of the light-scattering relaxation function broadened as the temperature approached the glass transition (Tg = 55°C). The average relaxation time shifted with temperature, consistent with previous studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was clearly bimodal and the shape altered with temperature. The higher frequency peak in the distribution corresponds well with previous mechanical and dielectric relaxation studies of the intramolecular relaxation of the acrylate ester side chain. The resolution of the distribution into two modes is due to a well-defined side-chain motion with relaxation strength comparable to the primary glass-rubber relaxation. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...