Comparison of DeltapH- and Delta***&phi;***-driven ATP synthesis catalyzed by the H(+)-ATPases from Escherichia coli or chloroplasts reconstituted into liposomes.
The H(+)-ATPases from Escherichia coli, EF(0)F(1), and from chloroplasts, CF(0)F(1), were reconstituted in liposomes from phosphatidylcholine/phosphatidic acid. The proteoliposomes were energized by an acid-base transition and a K(+)/valinomycin diffusion potential and the initial rate of ATP synthesis was measured as a function of the transmembrane pH difference, DeltapH, and the electric potential difference, Delta&phi;. With EF(0)F(1), a rate of 80 s(-1) is observed at DeltapH=4.1 and Delta&phi; approximately 140 mV. The rate decreases sigmoidally with Delta&phi; and at Delta&phi; approximately 0 mV, the rate is about 1 s(-1) although DeltapH is still 4.1. Under the same conditions with CF(0)F(1), a rate of 280 s(-1) is observed which decreases to 190 s(-1) when Delta&phi; is abolished, i.e. ATP synthesis catalyzed by EF(0)F(1) and CF(0)F(1) depends in a different way on DeltapH and Delta&phi;. EF(0)F(1)-catalyzed ATP synthesis was measured as a function of DeltapH at a constant Delta&phi;. The rate depends sigmoidally on DeltapH reaching a maximal rate which cannot be further increased by increasing DeltapH. However, this maximal rate depends on Delta&phi;, i.e. DeltapH and Delta&phi; are not kinetically equivalent in driving ATP synthesis. We assume that EF(0)F(1) must be converted into a metastable, active state before it catalyzes proton transport-coupled ATP synthesis. For EF(0)F(1), this activation step depends only on Delta&phi;, whereas for CF(0)F(1), the activation depends on DeltapH and Delta&phi;.
Fischer
S
S
Institut für Physikalische Chemie, Universität Freiburg, Albertstr. 23a, D-79104, Freiburg, Germany. fischsus@ruf.uni-freiburg.de
Gräber
P
P
D000255:Adenosine Triphosphate / Q000096:biosynthesis* / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology*; D004926:Escherichia coli / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D011189:Potassium Chloride / Q000737:chemistry; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D011522:Protons
D008081:Liposomes; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D011522:Protons; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases