 D. proOmpA preincubated at 37oC fails to stimulate SecA ATPase activity. proOmpA (0.5 μM) was either diluted directly (lane 1) or after preincubation alone (10 min; buffer D; < 0.2 M urea; either at 4°C or 37°C) into reactions containing SecYEG-SecA alone or together with TF2 or SecB4 (2 and 4 x molar excess over proOmpA, respectively). T/M ratios (as in Fig. 1D) are shown (n= 8 biological replicates; mean values ± SEM; Unpaired parametric t-test, 95% confidence interval: **: p = 0.0017; ****: p < 0.0001) 