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Abstract
The occurrence of Hofmeister (specific ion) effects in various membrane-related physiological processes is well documented. For example the effect of anions on the transport activity of the ion pump Na+, K+-ATPase has been investigated. Here we report on specific anion effects on the ATP-dependent Ca2+ translocation by the sarcoplasmic reticulum Ca2+-ATPase (SERCA). Current measurements following ATP concentration jumps on SERCA-containing vesicles adsorbed on solid supported membranes were carried out in the presence of different potassium salts. We found that monovalent anions strongly interfere with ATP-induced Ca2+ translocation by SERCA, according to their increasing chaotropicity in the Hofmeister series. On the contrary, a significant increase in Ca2+ translocation was observed in the presence of sulphate. We suggest that the anions can affect the conformational transition between the phosphorylated intermediates E1P and E2P of the SERCA cycle. In particular, the stabilization of the E1P conformation by chaotropic anions seems to be related to their adsorption at the enzyme/water and/or at the membrane/water interface, while the more kosmotropic species affect SERCA conformation and functionality by modifying the hydration layers of the enzyme.
Highlights
Order to reproduce specific ion effects in simulation studies[13,14], and in order to take into account ionic dispersion forces in the calculation and prediction of activity and osmotic coefficients[15]
Current is detected, which is related to the displacement of positive charge, i.e. Ca2+ ions, within the protein[35,36]. In this contribution we report on the current measurements following ATP concentration jumps on SERCA-containing vesicles adsorbed on solid supported membrane (SSM), in the presence of different potassium salts
We performed current measurements on native sarcoplasmic reticulum (SR) vesicles containing SERCA adsorbed on a SSM, in order to investigate the effect of different potassium salts on the ATP-dependent Ca2+ translocation by SERCA, keeping the cation (K+) constant
Summary
Order to reproduce specific ion effects in simulation studies[13,14], and in order to take into account ionic dispersion forces in the calculation and prediction of activity and osmotic coefficients[15]. The aim of the present research is to investigate specific ion effects on the pumping activity of the sarcoplasmic reticulum Ca2+-ATPase (SERCA). This technique has extensively been used to investigate the ion translocation mechanism of the SERCA pump[34,35,36,37,38,39,40]. By rapidly changing from a solution containing no substrate for the protein to one that contains a substrate, the protein can be activated and an electrical www.nature.com/scientificreports/
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