Activation of the H(+)-ATP synthase in the photosynthetic bacterium Rhodobacter capsulatus.
The regulation of the membrane-bound H(+)-ATPase from the photosynthetic bacterium Rhodobacter capsulatus was investigated. In the presence of uncouplers the rate of ATP hydrolysis was about 40 mM ATP/M bacteriochlorophyll (Bchl)/s. Without uncouplers this rate increased and if, additionally, the chromatophores were illuminated, it was almost doubled. If uncouplers were added shortly after illumination, the rate increased to 300-350 mM ATP/M Bchl/s. Obviously, energization of the membrane leads to the formation of a metastable, active state of the H(+)-ATPase. The maximal rate of ATP hydrolysis can be measured only when first all H(+)-ATPases are activated by delta mu H+ and when the delta mu H+ is abolished in order to release its back pressure on the hydrolysis rate. The half-life time of the metastable state in the absence of delta mu H+ is about 30 s. It is increased by 3 mM Pi to about 80 s and it is decreased by 1 mM ADP to about 15 s. Quantitatively, the fraction of active H(+)-ATPases shows a sigmoidal dependence on pHin (at constant pHout) and the magnitude of delta psi determines the maximal fraction of enzymes which can be activated: delta pH and delta psi are not equivalent for the activation process.
Turina
P
P
Max-Volmer Institut, Technische Universität Berlin, Germany.
Rumberg
B
B
Melandri
B A
BA
Gräber
P
P
D000227:Adenine Nucleotides / Q000494:pharmacology; D004789:Enzyme Activation; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008027:Light; D008564:Membrane Potentials; D010710:Phosphates / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D016354:Rhodobacter capsulatus / Q000201:enzymology* / Q000502:physiology
D000227:Adenine Nucleotides; D010710:Phosphates; D006180:Proton-Translocating ATPases