ИСТИНА

Noncompetitive inhibition of ATPase activity by MgADP is a common regulatory feature of all FoF1-ATP synthases studied so far. When MgADP is bound at a catalytic site without phosphate, a conformational transition may occur leading to complete enzyme inactivation. In chloroplasts, mitochondria, and some bacteria phosphate counteracts this inhibition and increases ATPase activity of FoF1. On the other hand, in Escherichia coli enzyme, phosphate inhibits ATPase activity and enhances MgADP-inhibition. In our previous work, we had described a single mutation, Leu249Gln, in beta subunit of E. coli ATP synthase, which completely changed the effect of phosphate on ATPase activity of inverted membrane vesicles. In this study, we demonstrate that purified E. coli F1 and FoF1 complexes containing this mutation are indeed activated or, at least, not inhibited by inorganic phosphate. Sulfite, which is known to relieve MgADP inhibition, has almost no effect on the wild-type enzyme, but stimulates ATP hydrolysis by the mutant complexes severalfold. The ATPase activity of the mutant complexes is also more susceptible to azide inhibition. We suggest that betaLeu249Gln FoF1 is inhibited by MgADP more pronouncedly than the wild-type complex. The relationship between MgADP, pmf, and phosphate in regard to E. coli FoF1-ATPase is also discussed.