ИСТИНА

Inside-out plasma vesicles of P.denitrificans are capable of either proton motive force (p.m.f.)-consuming ATP synthesis or (p.m.f.)-generating ATP hydrolysis [1]. The latter activity is under control of p.m.f.: it rapidly declines if p.m.f. drops down presumably because of the enzyme transformation to so-called ADP(Mg)-inhibited state [2,3]. Thus Fo·F1 serves as the p.m.f. utilizing and p.m.f. sensing device. Here we show that P.denitrificans Fo·F1 is also an efficient pH-sensor. The rate of couple d ATP hydrolysis decreases upon acidification corresponding to protonation of a single group with pKa equal to 7.2. The ATP synthase activity does not dependent on pH in 6.5-8.0 range as is expected if synthesis or hydrolysis of ATP is catalyzed by different “conformers” of Fo·F1 via different intermediates. A decrease of ATP hydrolytic activity upon acidification is neither due to accelerated transformation of the enzyme to its ADP(Mg)-inhibited state nor to decreased affinity to the substrate, ATP. Only Vmax, not Km for ATP is affected by pH. Fo·F1 activity is inevitably accompanied by acidification or alkalization of the medium (bacterial cytoplasm or mitochondrial matrix) because of scalar proton release or uptake depending on the direction of catalysis. Thus, in addition to its major bioenergetic function Fo·F1 may serve as an efficient dynamic pH-state