Figure 2. Effect of detergent concentration on pH-dependent modification and labeling kinetics of the isolated WT and P51A mutant B. pseudofirmus OF4 c₁₃ ing with dicyclohexylcarbodiimide (DCCD).

(A) pH-dependent modification of E⁵⁴ of the WT and P51A mutant with 375 μM DCCD at low and high dodecylmaltoside (DDM) detergent concentrations. At 0.05% DDM concentration the WT and the P51A c-ring mutant show a similar pH-dependent reaction profile, with fastest labeling at pH 7.5. In the presence of 3% DDM (same concentration used for 3D crystallization), DCCD modification was dramatically reduced, independent of the pH. DCCD reactions were carried out for 90 min for the WT and 15 min for P51A. (B) DCCD reaction kinetics of the isolated WT and P51A mutant c-ring. The labeling was performed at pH 7.5 using the same protein and DCCD concentrations as in (A), using 0.05% DDM. The P51A mutant c-ring showed much faster labeling kinetics compared with the WT c-ring. The standard deviation in both figures was calculated from at least three individual measurements.