Comparison of induced proteins synthesized in hydrogen peroxide and near-ultraviolet -treated bacterial cells
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I examined whether bacterial protein synthesis regulation in response to near-ultraviolet radiation (NUV) and hydrogen peroxide (H2 O2 ) occurs via common or separate biochemical pathways. My approach was to compare the proteins that were induced by the two agents, as well as the proteins that cease synthesis under these conditions, using two-dimensional polyacrylamide gel electrophoresis (PAGE). Also, specific comparisons were made of catalase (HPI and HPII) and superoxide dismutase (Fe2 + and Mn2 + ) following H2 O2 and NUV treatments by assaying one dimensional native disc gels after adding appropriate substrates and indicators. The strains compared were Escherichia coli and Salmonella typhimurium wildtype, mutants constitutively overexpressing proteins controlled by the oxyR regulon, and deletion mutants of oxyR. In the oxyR mutants that overexpress specific proteins constitutively, 11 newly synthesized proteins were induced by H2 O2 in S. typhimurium and 14 in E.coli in the initial 50 minutes following treatment. Eight and seven proteins were induced by NUV in S. typhimurium and E. coli, respectively. Of the 11 H2O2 -- induced and eight NUV-induced proteins in S. typhimurium, only one was common to both treatments. Thus, 10 proteins were exclusively induced by H2 O2 and seven by NUV. In E. coli similar results were observed; five proteins were induced only by NUV and 12 only by H2 O2 , but two induced proteins were common to both NUV and H2 O2 treatments. In E. coli and S.typhimurium oxyR deletion mutants, no overlap of newly induced polypeptide synthesis was observed. Moreover, inductional differences were observed in catalase and superoxide dismutase synthesis rates between NUV and hydrogen peroxide treated cultures. Catalase HPI activity was elevated in response to hydrogen peroxide treatment but was unaffected by NUV irradiation. Also, NUV induces both sodA and sodB. Hydrogen peroxide stress may repress Fe2 + SOD and may result in slightly increased Mn2 + SOD activity levels. These results indicate that H2 O2 and NUV damages induce a few common proteins, but also some proteins that are unique to each. The results suggest that NUV damage and recovery is only partially under the control of the oxidative stress regulon.
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