Monitoring genotoxicity during the photocatalytic degradation ofp-nitrophenol

p-Nitrophenol is a common structural unit of many pesticides and was chosen as a model compound to monitor genotoxicity during photocatalytic degradation. The genotoxicity of p-nitrophenol (PNP) and its breakdown products was measured using a bioluminescent bacterial bioassay, Vitotox. The genotoxic potential decreased with the concomitant photocatalytic degradation of the parent PNP concentration. The rate of genotoxicity reduction was slower than the rate of removal of the parent PNP, due to the formation of genotoxic by-products. After 6 h of photocatalytic treatment the total genotoxicity was removed. These results indicate that bioassays can be used as a simple and highly sensitive method for monitoring the general toxicity of chemical pollutants before, during and after photocatalytic treatment or other destructive processes.

Mutation in the lumenal part of the membrane domain of HMG-CoA reductase alters its regulated degradation

The involvement of ER lumenal domains of HMG-CoA reductase in the regulated degradation process was examined. For this purpose we studied three cell lines expressing HMG-CoA reductase molecules with introduced functional N-glycosylation sites located in the linker segments between transmembrane spans 1 and 2 (HMGal/Bins(-)), 3 and 4 (HMGal/Dins(-)) and 5 and 6 (HMGal/Fins(-)), all facing the ER lumen (Olender, E. H. and Simoni, R. D. (1992) J. Biol. Chem. 267, 4223-4235. The glycosylation insertion between spons 5 and 6 (HMGal/Fins(-)) is the only one of these mutations which eliminates regulated degradation of the enzyme. The half lives of the HMGal/Fins(-) in the presence or absence of regulatory molecules are indistinguishable. In contrast the HMGal/Bins(-) and HMGal/Dins(-) mutants show a normal pattern of regulated degradation. Tunicamycin treatment of cells expressing the HMGal/Fins(-) mutant does not significantly alter the regulation defect indicating that it is the mutation per se not the glycosylation that alters the degradation response. These results suggest that the linker segments between transmembrane spans 5 and 6 (loop F) are involved in the process of regulated degradation of HMG-CoA reductase and that the regulated degradation process may occur on the lumenal side of the ER membrane.