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Biomedical subjects

K W Thomulka

Publications and source records attributed to K W Thomulka.

29 records · Page 2Linked to original sources
PubMed1996

A mixture toxicity study employing combinations of tributyltin chloride, dibutyltin dichloride, and tin chloride using the marine bacterium Vibrio harveyi as the test organism.

Mixture toxicity studies in dual combinations for three metals, tributyltin chloride, dibutyltin dichloride, and tin chloride, and one experiment using all chemicals were performed using the bioluminescent marine bacterium Vibrio harveyi as the test organism in a direct toxicity test procedure. Combination toxicity was evaluated using an additive index equation method and two isopleth procedures, isobole plot and isobologram. Additive index values were determined at both estimated effective median concentration (EC50) and one-third EC50 values for each dual combination and all three chemicals for one-third EC50 values. Isopleths employed chemical combinations at 20% intervals of the EC50 concentrations. Additive index values for various mixtures were either additive or antagonistic (less than additive). Isobolograms for all mixtures were descriptively additive or synergistic (greater than additive). Isobole plots were also descriptively additive or synergistic, although a few measurements were statistically different for synergism. Statistical evaluation between mixtures and single values, using the z test, were in some cases different at the 5% level. Bioluminescent counts were determined to be normally distributed using a statistical test for small sample numbers at the 1% level. Evaluation for outliers, using the Dixon test, was also performed and found one mixture to have an outlier. This single outlier had no influence on the combined toxicity results. The use of low-cost and rapid bioluminescent microbial toxicity tests for mixture studies is discussed.

Drug Interactions↗
PubMed1996

A study of personal and area airborne asbestos concentrations during asbestos abatement: a statistical evaluation of fibre concentration data.

Data were collected and analysed on airborne concentrations of asbestos generated by abatement of different asbestos-containing materials using various removal practices. Airborne concentrations of asbestos are dramatically variable among the types of asbestos-containing material being abated. Abatement practices evaluated in this study were removal of boiler/pipe insulation in a crawl space, ceiling tile, transite, floor tile/mastic with traditional methods, and mastic removal with a high-efficiency particulate air filter blast track (shot-blast) machine. In general, abatement of boiler and pipe insulation produces the highest airborne fibre levels, while abatement of floor tile and mastic was observed to be the lowest. A comparison of matched personal and area samples was not significantly different, and exhibited a good correlation using regression analysis. After adjusting data for outliers, personal sample fibre concentrations were greater than area sample fibre concentrations. Statistical analysis and sample distribution of airborne asbestos concentrations appear to be best represented in a logarithmic form. Area sample fibre concentrations were shown in this study to have a larger variability than personal measurements. Evaluation of outliers in fibre concentration data and the ability of these values to skew sample populations is presented. The use of personal and area samples in determining exposure, selecting personal protective equipment and its historical relevance as related to future abatement projects is discussed.

Air Pollutants, Occupational↗
PubMed1995

Use of the bioluminescent bacterium Vibrio harveyi to detect biohazardous chemicals in soil and water extractions with and without acid.

An investigation was undertaken using the bioluminescence-reduction bioassay of Vibrio harveyi to study the toxicity of 31 chemicals in a soil and water extraction that was treated with and without hydrochloric acid. Soil had the chemical added and was washed with 0.2 N HC1 and afterward this acid-treated soil containing the chemical was evaluated. Each chemical was tested independently. Endpoints determined were either an estimated effective concentration at 50 or 20%, which was based on bacterial-luminescence remaining after treatment. This investigation suggests that metals are more effectively bound in treatments without acid than those with acid, while no difference in toxicity was observed for organics. In comparison to a previous study of toxicity using these chemicals in water, soil was effective in reducing toxicity as determined by this assay. However, each chemical appears to have its own unique toxicity characteristic when evaluated under different conditions.

Biodegradation, Environmental↗
PubMed1982

Isolation and characterization of purine regulatory mutants of Salmonella typhimurium with an episomal purE-lac fusion.

Expression of the purE operon of Salmonella typhimurium was analyzed by using an Escherichia coli F' episome containing a purE-lac fusion. The fusion removes the lacOP and part of the lacZ genes of the lac operon and places the intact lacY and lacA genes under control of the purE operon as shown by inhibition of growth on melibiose (lacY) and repression of thiogalactoside transacetylase (lacA) by various purines. Two classes of regulatory-deficient mutants were found among those resistant to inhibition by purines. One class was trans active (chromosomal) and corresponded to previously described purR mutants involving a deficient cytoplasmic repressor substance. These were also altered in the expression of the purF, purD, purG amd purI genes as evidenced by loss of repressibility of the synthesis of glycinamide ribotide and aminoimidazole ribotide. The other class was cis active (episomal), specific for only purE expression, and thus corresponded to an altered purE operon signal (operator or promoter). The metabolic requirements for the expression of purE were also monitored by measuring repression of the transacetylase in strains with various genetically altered metabolic backgrounds. Repression by guanine required an intact guanine phosphorbosyltransferase (gpt) and repression by adenine and all nucleosides required purine nucleoside phosphorylase (deoD). Synthesis of cyclic AMP (cya) and its receptor protein (crp) were no longer required for the expression of the lac genes under purE control.

Acetyltransferases↗
PubMed1972

Inorganic nitrogen assimilation in yeasts: alteration in enzyme activities associated with changes in cultural conditions and growth phase.

Ammonia assimilation has been investigated in four strains of Saccharomyces cerevisiae by measuring, at intervals throughout the growth cycle, the activities of several enzymes concerned with inorganic ammonia assimilation. Enzyme activities in extracts of cells were compared after growth in complete and defined media. The effect of shift from growth in a complete to growth in a defined medium (and the reverse) was also determined. The absence of aspartase (EC 4.3.1.1, l-aspartate-ammonia lyase) activity, the low specific activities of alanine dehydrogenase, glutamine synthetase [EC 6.3.1.2, l-glutamate-ammonia ligase (ADP)], and the marked increase in activity of the nicotinamide adenine dinucleotide phosphate-linked glutamate dehydrogenase (NADP-GDH) [EC 1.4.1.4, l-glutamate:NADP-oxidoreductase (deaminating)] during the early stages of growth support the conclusion that yeasts assimilate ammonia primarily via glutamate. The NADP-GDH showed a rapid increase in activity just before the initiation of exponential growth, reached a maximum at the mid-exponential stage, and then gradually declined in activity in the stationary phase. The NADP-GDH reached a higher level of activity when the yeasts were grown on the defined medium as compared with complete medium. The nicotinamide adenine dinucleotide-linked glutamate dehydrogenase (NAD-GDH) [EC 1.4.1.2, l-glutamate:NAD-oxidoreductase (deaminating)] showed only slight increases in activity during the exponential phase of growth. There was an inverse relationship in that the NADP-GDH increased in activity as the NAD-GDH decreased. The NAD-GDH activity was higher after growth on the complete medium. The glutamate-oxaloacetate transaminase (EC 2.6.1.1. l-aspartate:2-oxoglutarate aminotransferase) activity rose and fell in parallel with the NADP-GDH, although its specific activity was somewhat lower. Although other ammonia-assimilatory enzymes were demonstrable, it seems unlikely that their combined activities could account for the remainder of the ammonia-assimilatory capacity not accounted for by the NADP-GDH. The ability of aspartate to serve as effectively as glutamate as the sole source of nitrogen for the growth of yeast apparently resides in their ability to utilize aspartate for amino acid biosynthesis via transamination.

Alanine↗