FIGURE 4.

IbpB protects representative metabolic enzymes from stress-induced inactivation. A, relative levels of catalase activity of the wild-type and ΔibpB cells (from three independent assays). Cells were heat-shocked at 50 °C for 0.5 h and/or treated with 5 mm H₂O₂ for 0.5 h, sonicated, and centrifuged. Cell extracts were then subjected to catalase activity assay as described under “Experimental Procedures.” B, immunoblotting detection of carbonylated proteins in the wild-type and ΔibpB cells after heat shock at 50 °C for 0.5 h and/or treatment with 5 mm H₂O₂ for 0.5 h. Protein bands with a higher level of carbonylation signals in ΔibpB cells than that in wild-type cells are indicated by asterisks. EF-Tu was immunoblotted as a loading control.