Physiological ligands ADP and Pi modulate the degree of intrinsic coupling in the ATP synthase of the photosynthetic bacterium Rhodobacter capsulatus.
The proton-pumping and the ATP hydrolysis activities of the ATP synthase of Rhodobacter capsulatus have been compared as a function of the ADP and P(i) concentrations. The proton pumping was measured either with the transmembrane pH difference probe, 9-amino-6-chloro-2-methoxyacridine, or with the transmembrane electric potential difference probe, bis(3-propyl-5-oxoisoxazol-4-yl)pentamethine oxonol, obtaining consistent results. The comparison indicates that an intrinsic uncoupling of ATP synthase is induced when the concentration of either ligand is decreased. The half-maximal effect was found in the submicromolar range for ADP and at about 70 microM for P(i). It is proposed that a switch from a partially uncoupled state of ATP synthase to the coupled state is induced by the simultaneous binding of ADP and P(i).
Turina
Paola
P
Department of Biology, Laboratory of Biochemistry and Biophysics, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy. turina@alma.unibo.it
Giovannini
Donatella
D
Gubellini
Francesca
F
Melandri
B Andrea
BA
D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000609:Aminoacridines / Q000378:metabolism; D001665:Binding Sites; D025222:Chloroplast Proton-Translocating ATPases / Q000737:chemistry / Q000378:metabolism*; D022162:Cytoplasmic Vesicles / Q000201:enzymology; D006868:Hydrolysis; D007555:Isoxazoles / Q000378:metabolism; D008024:Ligands; D009995:Osmosis; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D010788:Photosynthesis; D011770:Pyruvate Kinase / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000201:enzymology* / Q000254:growth & development
D000609:Aminoacridines; D007555:Isoxazoles; D008024:Ligands; D010710:Phosphates; C010847:9-amino-6-chloro-2-methoxyacridine; D000244:Adenosine Diphosphate; C031184:oxonol VI; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D025222:Chloroplast Proton-Translocating ATPases