Search results for "Reversion"
showing 10 items of 20 documents
The presence of KCl in the exposure medium strongly influences the mutagenicity of metabolites of polycyclic aromatic hydrocarbons in Escherichia col…
1994
Abstract Previous studies demonstrated that the ion composition of the exposure medium may strongly influence the mutagenicity of many compounds in the liquid preincubation modification of the reversion assay with his − Salmonella typhimurium strains. Similar influences were now observed in the reversion assay with trp − Escherichia coli strain WP2 uvrA . The exposure medium was 8 mM sodium phosphate buffer (pH 7.4), containing no other ions or 125 mM KCl. Omission of KCl resulted in an about 10-fold enhancement of the mutagenic activity of 7-methylbenz[ a ]anthracene 5,6-oxide, but in a strong decrease in the mutagenicity of 1-hydroxymethylpyrene sulphate, close to the limit of detection. …
Structure-Activity Relations of Flavonoids as Antimutagens Against Cooked Food Mutagens and Nitroarenes in the Salmonella Reversion Assay
1997
When about 60 flavonoids were tested for their antimutagenic potencies against 2-amino-3-methylimidazo [4,5-f]quinoline (IQ) and the nitroarenes 2-nitrofluorene (2-NF), 1-nitropyrene (1-NP), and 3-nitrofluoranthene (3-NFA) in the Salmonella reversion assay, distinct structure-activity relations were detected. With both groups of compounds, flavonoid glycosides were inactive or at best weakly active. Catechins and anthocyanidins, which lack the carbonyl function at C-4 of the flavane nucleus, were inactive. In contrast, chalcones exerted strong antimutagenicity against IQ and the nitroarenes. With respect to IQ, flavonoids of low polarity were the most active compounds: The parent compounds …
SECULAR MEAN REVERSION AND LONG-RUN PREDICTABILITY OF THE STOCK MARKET
2016
Empirical financial literature documents the evidence of mean reversion in stock prices and the absence of out-of-sample return predictability over periods shorter than 10 years. The goal of this paper is to test the random walk hypothesis in stock prices and return predictability over periods longer than 10 years. Specifically, using 141 years of data, this paper begins by performing formal tests of the random walk hypothesis in the prices of the real S&P Composite Index over increasing time horizons up to 40 years. Even though our results cannot support the conventional wisdom which says that the stock market is safer for long-term investors, our findings speak in favor of the mean revers…
Is the environmental performance of industrialized countries converging? A ‘SURE’ approach to testing for convergence
2008
In this paper, we test for convergence in the environmental performance of a sample of OECD countries, with data ranging from 1971 to 2002. First, we use Data Envelopment Analysis (DEA) to compute two environmental performance indicators (EPIs) in the production theory framework. Second, we propose the use of a sequential multivariate approach to test for convergence in environmental performance. These tests allow us to reconcile the time series literature with the cross-sectional dimension, which is basic when testing for convergence in regional blocs. The SURE technique is used, which allows for the existence of correlations across the series without imposing a common speed of mean revers…
A critical empirical study of three electricity spot price models
2012
We conduct an empirical analysis of three recently proposed and widely used models for electricity spot price process. The first model, called the jump-diffusion model, was proposed by Cartea and Figueroa (2005), and is a one-factor mean-reversion jump-diffusion model, adjusted to incorporate the most important characteristics of electricity prices. The second model, called the threshold model, was proposed by Roncoroni (2002) and further developed by Geman and Roncoroni (2006), and is an exponential Ornstein–Uhlenbeck process driven by a Brownian motion and a state-dependent compound Poisson process. It is designed to capture both statistical and pathwise properties of electricity spot pri…
Cytogenetic manifestations associated with the reversion, by gene amplification, at the HGPRT locus in V79 Chinese hamster cells.
1989
SummarySome HGPRT spontaneous revertants were isolated from a mutant line (E2) of V79 Chinese hamster cells and phenotypically characterized. Dot–Blot hybridization with a32P-Iabelled HGPRT probe revealed an increase in the number of HGPRT sequences in some of these revertants, suggesting the occurrence of gene amplification. Cytogenetic analysis performed in three of these revertants showed a characteristic abnormally banding region (ABR) on the elongated p arm of theXchromosome.In Situhybridization in one revertant (RHE2) showed that the amplified sequences reside on the p+arm of theXchromsome in two different localizations. Because of the very probable clonal origin of the revertant, the…
Disaggregate Real Exchange Rate Behaviour
2007
In this paper, we re-examine the “PPP Puzzle” using sectoral disaggregated data. Specifically, we first analyse the mean reversion speeds of real exchange rates for a number of different sectors in eleven industrial economies and then focus on relating these rates to variables identified in the literature as key determinants of CPI-based real exchange rates, namely: the trade balance, productivity and the mark up. In particular, we seek to understand to what extent the relationships existing at the aggregate level are borne out at the disaggregate level. We believe that this analysis can help shed light on the PPP puzzle.
Modulation of induced reversion frequency by nucleotide pool imbalance as a tool for mutant characterization.
1987
Addition of thymidine (TdR) or deoxycytidine (CdR) to the culture medium during posttreatment incubation affected the frequency of mutagen-induced reversion in three hypoxanthine-guanine phosphoribosyl transferase-deficient mutants of V79 Chinese hamster cells. With two of the mutants (E20 and I3), reversions induced by N-ethylnitrosourea, ethyl methanesulfonate, and methyl methanesulfonate were enhanced by TdR and were either decreased (E20) or not affected (I3) by CdR. With the third mutant (E21), alkylating agent-induced reversions were enhanced by CdR and decreased by TdR. Finally, 6-amino-2-hydroxypurine induced reversions were enhanced by TdR in mutant I3 and were decreased by TdR or …
Clavine alkaloids and derivatives as mutagens detected in the Ames test.
1992
Eight cytostatic clavines were investigated for mutagenicity in Salmonella typhimurium (reversion of the his-strains TA98, TA100, TA102 and TA1537), directly and in the presence of a mammalian xenobiotic metabolizing system, S9 (NADPH-fortified postmitochondrial fraction of liver homogenate from Aroclor 1254-treated rats). Four compounds (festuclavine, 17-bromofestuclavine, 1-allylelymoclavine and 1-methyllysergol methyl ether) were direct mutagens, whose activity was enhanced in the presence of S9. The other compounds (1-cyclopentylfestuclavine, 13-bromo-1-cyclopropylmethylfestuclavine, 6-cyano-1-propyl-6-norfestuclavine and 6-allyl-1-propyl-6-norfestuclavine) showed mutagenic effects only…
Propyldazine is mutagenic inSalmonella typhimurium and Escherichia coli: Distinct specificity for strains TA1537 AND TA97
1985
The antihypertensive drug propyldazine (Atensil) was demonstrated to be muta- genic with auxotrophic mutants of Salmonella typhimurium and Escherichia coli. Addition of liver S9 mix (postmitochondrial supernatant fraction supplemented with an NADPH-generating system) had little, if any, effect on the mutagenicity. The mutagenicity showed an unusual pattern of strain specificity. Increased fre- quencies of reversion were observed with all strains whose auxotrophy was caused by frame-shift mutations: the number of revertant colonies per plate from S. typhimurium TA98, TA1538, TA97, and TA1537 was increased up to 5-, 9-, 43-, and 160-fold, respectively, above background. Among the strains that…