FIG. 5.
Effect of NaCl on DCCD inhibition of the purified F1Fo-ATPase. The purified ATPase (25 μg) was incubated at 25°C in 50 mM MOPS (pH 7.5) with increasing concentrations of DCCD for 20 min in the absence of NaCl (A) or in 50 mM MOPS (pH 7.5) and 200 μM DCCD (B). To examine the effect of pH and Na+ ions on DCCD inhibition, the ATPase was incubated in 50 mM MOPS (pH 7.0) (C) or 50 mM Tricine-KOH (pH 9.0) in the presence of 200 μM DCCD (D). The following additions of NaCl were made: none (•), 150 μM NaCl (○), 1 mM NaCl (▵), 10 mM NaCl (□), or 50 mM NaCl (▴). The control sample in the presence of an equivalent amount of ethanol (0.2%) contained no NaCl and no DCCD (▪). ATPase activity was determined as described in Materials and Methods; 100% ATPase activity was in the range of 15 to 20 U/mg protein.