Kinetics of luminal proton binding to the SR Ca-ATPase


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FIBICH, Andreas, Hans-Jürgen APELL, 2011. Kinetics of luminal proton binding to the SR Ca-ATPase. In: Biophysical Journal. 101(8), pp. 1896-1904. ISSN 0006-3495. eISSN 1542-0086. Available under: doi: 10.1016/j.bpj.2011.09.014

@article{Fibich2011-10-19Kinet-16381, title={Kinetics of luminal proton binding to the SR Ca-ATPase}, year={2011}, doi={10.1016/j.bpj.2011.09.014}, number={8}, volume={101}, issn={0006-3495}, journal={Biophysical Journal}, pages={1896--1904}, author={Fibich, Andreas and Apell, Hans-Jürgen} }

2011-10-19 eng Fibich, Andreas Apell, Hans-Jürgen First publ. in: Biophysical Journal ; 101 (2011), 8. - pp. 1896-1904 Fibich, Andreas terms-of-use Apell, Hans-Jürgen Kinetics of luminal proton binding to the SR Ca-ATPase 2012-01-05T12:04:17Z 2012-09-30T22:25:05Z An open membrane preparation containing SR Ca-ATPase was prepared from sarcoplasmic-reticulum vesicles to study the ion binding kinetics in the P-E2 conformation. Because Ca2+ and H+ binding are electrogenic reactions, fluorescent styryl dyes could be used to determine changes in the binding site occupation in equilibrium titration experiments and time-resolved relaxation processes triggered by a pH jump. By photo release from caged proton the pH of the electrolyte could be decreased in a step of 0.1 pH units by a single ultraviolet-laser flash. Analysis of the pH-jump induced relaxation process in the P-E2 conformation showed that three Ca-ATPase-specific processes could be identified, fast H+ binding (τ < 100 μs) and pH-insensitive conformational relaxations after the release of the Ca2+ ion (τ ∼160 ms), and a slow process (τ ∼3.4 s) whose origin could not be unambiguously revealed. The Ca2+-binding affinity in the P-E2 conformation was reduced with increasing pH, a behavior that can be explained by a reversible transition of the empty P-E2 state to an inactivated state of the ion pump. All findings are interpreted in the framework of the Post-Albers pump cycle introduced previously, supplemented by an additional transition to an inhibited state of the ion pump.

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