Membrane-bound adenosine triphosphatase of Escherichia coli. III. Effects of sodium azide on the enzyme functions.

1. Sodium azide and diphenyl phosphorazidate (DPPA) inhibited purified membrane-bound ATPase [coupling factor of oxidative phosphorylation; EC 3.6.1.3] of Escherichia coli non-competitively with Ki values of 39 and 51 micrometer, respectively. 2) Sodium azide and DPPA inhibited the activity of ATPase bound to the membrane as effectively as that of the purified enzyme. 3) The effects of sodium azide on succinate-dependent ATP synthesis, Pi-ATP exchange, and ATP hydrolysis reactions by the membrane vesicles were compared under the same conditions. At concentrations below 1.0 mM, sodium azide inhibited ATP hydrolysis, but Pi-ATP exchange and ATP synthesis were almost unaffected. At 10 mM sodium azide, both Pi-ATP exchange and ATP synthesis reactions were completely inhibited, probably because at this concentration, sodium azide acted as a proton-conducting uncoupler.