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).
Department of Biology, Laboratory of Biochemistry and Biophysics, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy. turina@alma.unibo.it
Paola
P
Turina
Donatella
D
Giovannini
Francesca
F
Gubellini
B Andrea
BA
Melandri
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