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Role of Protons in the Pump Cycle of KdpFABC Investigated by Time-Resolved Kinetic Experiments

Role of Protons in the Pump Cycle of KdpFABC Investigated by Time-Resolved Kinetic Experiments

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DAMNJANOVIC, Bojana, Hans-Jürgen APELL, 2014. Role of Protons in the Pump Cycle of KdpFABC Investigated by Time-Resolved Kinetic Experiments. In: Biochemistry. 53(19), pp. 3218-3228. ISSN 0006-2960. eISSN 1520-4995. Available under: doi: 10.1021/bi500336w

@article{Damnjanovic2014-05-20Proto-27910, title={Role of Protons in the Pump Cycle of KdpFABC Investigated by Time-Resolved Kinetic Experiments}, year={2014}, doi={10.1021/bi500336w}, number={19}, volume={53}, issn={0006-2960}, journal={Biochemistry}, pages={3218--3228}, author={Damnjanovic, Bojana and Apell, Hans-Jürgen} }

Apell, Hans-Jürgen 2014-05-28T13:15:17Z 2014-05-28T13:15:17Z The time-resolved kinetics of the KdpFABC complex solubilized in Aminoxide WS-35 was investigated by ATP concentration jump experiments. ATP was photoreleased from its inactive precursor, caged ATP, and charge movements in the membrane domain of the KdpFABC were detected by the electrochromic dye RH421. At low ATP concentrations, the ATP binding step became rate-limiting with an apparent, pH-independent ATP binding affinity of ~70 μM. At saturating ATP concentrations, the rate-limiting step is the conformational transition (E1-P → P-E2) with a rate constant of ~1.7 s(-1) at 20 °C that was independent of K(+) concentration. This observation together with the detected fluorescence decrease indicates that K(+) (or another positive ion) is bound in the membrane domain after enzyme phosphorylation and the conformational transition to the P-E2 state. pH dependence experiments revealed different roles of H(+) in the transport mechanism. Two different functions of protons for the ion pump must be distinguished. On one hand, there are electrogenically bound "functional" protons, which are not transported but prerequisite for the performance of the ATP-driven half-cycle. On the other hand, protons bind to the transport sites, acting as weak congeners of K(+). There possibly are noncompetitively bound protons, affecting the enzyme activity and/or coupling between KdpA and KdpB subunits. Finally, the recently proposed Post-Albers model for the KdpFABC complex was supplemented with stoichiometry factors of 2 for K(+) and 3 for H(+), and additional inhibitory side reactions controlled by H(+) were introduced, which are relevant at pH <6.5 and/or in the absence of K(+). Biochemistry ; 53 (2014), 19. - S. 3218-3228 Role of Protons in the Pump Cycle of KdpFABC Investigated by Time-Resolved Kinetic Experiments eng 2014-05-20 Damnjanovic, Bojana Damnjanovic, Bojana Apell, Hans-Jürgen deposit-license

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