TI - Response of flagellin , OppA and GltI to H2O2 is altered in the DeltaarcA mutant E.coli . . AB - To investigate the mechanisms of H2O2 resistance mediated by ArcA , we performed two-dimensional gel electrophoresis to examine the protein profiles in the DeltaarcA mutant E.coli in the presence or absence of H2O2 , and compared to those of the wild type E.coli . While most proteins either were not altered by H2O2 treatment , or responded similarly to H2O2 treatment in the wild type and DeltaarcA mutant E.coli , the levels of three proteins were observed to respond to H2O2 differently , the most abundant of which is shown in Figure 4 . By peptide mass fingerprinting using MALDI-TOF , the prominent protein in Figure 4 was identified as flagellin encoded by fliC , while the other two less abundant proteins were identified as oligopeptide ABC transporter SUBstrate-binding protein ( OppA ) and glutamate and aspartate transporter subunit ( GltI ) ( data not shown ) . The levels of these proteins were quantified in the H2O2-treated and control untreated samples of the wild type and DeltaarcA mutant E.coli ( Table 2 ) . Flagellin is the only one among the 10 most abundant proteins that responded to H2O2 treatment . In the wild type , un-treated E.coli flagellin was detected at a lower level than in the DeltaarcA mutant E.coli and H2O2 treatment further decreased the flagellin level ( p lt 005 , Student's t-test , Table 2 and Figure 4 ) . In the DeltaarcA mutant E.coli H2O2 treatment also decreased flagellin level , however , the decrease was not statistically significant ( Table 2 ) . Therefore , compared to the wild type the E.coli , DeltaarcA mutant displayed higher flagellin levels both constitutively and following H2O2 treatment , and its flagellin level did not respond to H2O2 treatment as that in the wild type E.coli . The response of OppA and GltI expression was different from that of flagellin . In the untreated bacteria levels of both GltI and OppA appeared to be higher in the DeltaarcA mutant than in the wild type E.coli ( p lt 005 , Student's t-test for GltI , Table 2 ) . Following H2O2 treatment the levels of OppA and GltI in the wild type E.coli became higher ( p lt 005 , Student's t-test ) , while neither protein displayed a statistically significant change in the DeltaarcA mutant E.coli ( Table 2 ) . This results in a lower GltI and OppA level in the H2O2 treated DeltaarcA mutant than the wild type E.coli .