Prokaryotic assay systems

Genotoxic Effects. No studies were located regarding the genotoxic effects of hexachloroethane in humans after inhalation, oral, or dermal exposure. In vitro studies of hexachloroethane using microbial, fungal, and rodent cell assays are summarized in Table 2-4. Tests of prokaryotic cell systems failed to detect gene mutation (Haworth et al. 1983 Roldan-Arjona et al. 1991 Simmon and Kauhanen 1978 ... 

Studies on the genotoxicity of methoxychlor have generally yielded negative results in prokaryotic assays, mixed results in in vitro eukaryotic systems, and negative results in in vivo studies. ... 

Methyl parathion has been tested in numerous genotoxicity assays using prokaryotic and eukaryotic systems with both positive and negative results. Results of these studies are summarized in Tables 3-5 and 3-6. 

Mustard gas is highly genotoxic. In vitro assays in both prokaryotic and eukaryotic systems support a mechanism of DNA alkyla-... 

MARA is an innovative bioassay devised for the evaluation of toxicity of chemicals and environmental samples. The assay utilizes a taxonomically diverse array of ten bacterial species (prokaryotes) and a yeast (eukaryote). The assay is performed in a 96 well micro titre plate and involves exposure of the microorganisms provided in a freeze-dried state. The toxicity of the test sample using a concentration gradient is determined with the employment of the redox dye tetrazolium red (TZR). The dye is transformed from a soluble colourless state to a red insoluble form upon reduction. The dye is a growth indicator and detects enzyme systems by acting as an electron acceptor. 

Prokaryotic promoters. Prokaryotic systems are generally used for rapid screening assays. A well established example is the Ames test that was developed with Salmonella in the 1970s (Ames, 1979 McDaniels et al., 1990 Reifferscheid and Heil, 1996) and is still considered as the standard mutagenicity assay. 

Although there is less biochemical information on secretion in prokaryotes, genetic data indicate that the process is likely to be similar to that in eukaryotes. The development of in vitro translocation assays for bacterial systems (Muller and Blobel, 1984a,b Rhoads et al., 1984 Chen et al., 1985) should allow a more detailed analysis of the biochemistry of prokaryotic secretion in the near future. 

Theaflavins efficiently and specifically inhibited the proteasomal chymotrypsin-like activity of the purified mammalian 20S and 26S proteasomes in cell-free systems (figure 11.3) as well as 26S proteasomes in tumor cell extracts (table 11.1). The purified M. thermophila recombinant 20S proteasome was more sensitive to theaflavins than mammalian 20S or 26S proteasomes, possibly due to prokaryotic recombinant 20S proteasome without postmodification that forms steric hindrance that prevents theaflavins from binding to the chymotrypsin-like activity subunit of the 20S proteasome. When assaying for proteasomal chymotrypsin-like activity in human cancer cell extracts, the IC50 values of tea polyphenols were apparently increased compared... 

Widespread use of the yeast two-hybrid system led several groups to develop alternate transcription-based assays. While the yeast two-hybrid assay is quite powerful, a bacterial equivalent would increase by several orders of magnitude the number of proteins that could be tested, as the transformation efficiency and doubling rate of E. coli are significantly greater than those of S. cerevisiae. There may also be applications where it is advantageous to test a eukaryotic protein in a prokaryotic environment, in which many pathways are not conserved. The yeast two-hybrid assay cannot, however, be transferred directly to bacteria since the components of the transcription machinery and the mechanism of transcriptional activation differ significantly between bacteria and yeast. 

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