Kinetics and ion specificity of Na/Ca exchange mediated by the reconstituted beef heart mitochondrial Na/Ca antiporter |
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Authors: | Petr Paucek Martin Jab?rek |
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Institution: | a Department of Biology, Portland State University, Portland, Oregon 97207, USA b Department of Membrane Transport Biophysics, Institute of Physiology, Acadeny of Sciences of the Czech Republic, Videnska 1083, 14220 Prague, Czech Republic |
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Abstract: | The Na+/Ca2+ antiporter was purified from beef heart mitochondria and reconstituted into liposomes containing fluorescent probes selective for Na+ or Ca2+. Na+/Ca2+ exchange was strongly inhibited at alkaline pH, a property that is relevant to rapid Ca2+ oscillations in mitochondria. The effect of pH was mediated entirely via an effect on the Km for Ca2+. When present on the same side as Ca2+, K+ activated exchange by lowering the Km for Ca2+ from 2 to 0.9 μM. The Km for Na+ was 8 mM. In the absence of Ca2+, the exchanger catalyzed high rates of Na+/Li+ and Na+/K+ exchange. Diltiazem and tetraphenylphosphonium cation inhibited both Na+/Ca2+ and Na+/K+ exchange with IC50 values of 10 and 0.6 μM, respectively. The Vmax for Na+/Ca2+ exchange was increased about fourfold by bovine serum albumin, an effect that may reflect unmasking of an autoregulatory domain in the carrier protein. |
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Keywords: | BSA bovine serum albumin EGTA ethylene-bis(oxyethylenenitrilo) tetraacetic acid HEDTA N-(2-hydroxyethyl)ethylenediamine-N N&prime N&prime -triacetic acid SBFI sodium-binding benzofuran isophthalate SMPs submitochondrial particles TEA+ tetraethylammonium cation TES N-tris(hydroxymethyl)methylaminoethenesulfonic acid TPP+ tetraphenylphosphonium XIP exchange inhibitory peptide |
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