Chromium(III)ATP inactivating (Na++ K+)‐ATPase supports Na+‐Na+ and Rb+‐Rb+ exchanges in everted red blood cells but not Na+,K+ transport
- 1 June 1986
- journal article
- research article
- Published by Wiley in European Journal of Biochemistry
- Vol. 157 (3) , 585-595
- https://doi.org/10.1111/j.1432-1033.1986.tb09706.x
Abstract
1. The chromium(III) complex of ATP, and MgATP complex analogue, inactivates (Na+ + K+)-ATPase by forming a stable chromo-phosphointermediate. The rate constant k2 of inactivation at 37.degree. C of the .beta.,.gamma.-bidentate of CrATP is enhanced by Na+ (Ko.5 = 1.08 mM), imidazole (K0.5 = 15 mM) and Mg2+ (K0.5 = 0.7 mM). These cations did not affect the dissociation constant of the enzyme-chromium-ATP complex. 2. The inactive chromophosphoenzyme is reactivated slowly by high concentrations of Na+ at 37.degree. C. The half-maximal effect on the reactivation was reached at 40 mM NaCl, when the maximally observable reactivation was studied. However, 126 mM NaCl was necessary to see the half-maximal effect on the apparent reactivation velocity constant. K+ ions hindered the reactivation with a Ki of 70 .mu.M. 3. Formation of the chromophosphoenzyme led to a reduction of the Rb+ binding sites and of the capacity to occlude Rb+. 4. The .beta.,.gamma.-bidentate of chromium(III)ATP (Kd - 8 .mu.M) had a higher affinity than the .alpha.,.beta.,.gamma.-tridentate of chromium(III)ATP (Kd = 44 .mu.M) or the cobalt tetramine complex of ATP (Kd = 500 .mu.M). The .beta.,.gamma.-bidentate of the chromium(III) complex of adenosine 5''-[.beta.,.gamma.-methylene]triphosphate also inactivated (Na+ + K+)ATPase. 5. Although CrATP could not support Na+,K+ exchange in everted vesicles prepared from human red blood cells, it supported the Na+-Na+ and Rb+-Rb+ exchange. 6. It is concluded that CrATP opens up Na+ and K+ channels by forming a relatively stable modified enzyme-CrATP complex. This stable complex is also formed in the presence of the chromium complex of adenosine 5''-[.beta.,.gamma.-methylene]triphosphate. Because the .beta.,.gamma.-bidentate of chromium ATP is recognized better than the .alpha.,.beta.,.gamma.-tridentate, it is concluded that the triphosphate site recognizes MgATP with a straight polyphosphate chain and that the Mg2+ resides between the .beta.- and the .gamma.-phosphorus. The enhancement of inactivation by Mg2+ and Na+ may be caused by conformational changes at the triphosphate site.Keywords
This publication has 51 references indexed in Scilit:
- Demonstration of an Mg2+‐induced conformational change by photoaffinity labelling of the high‐affinity ATP‐binding site of (Na++ K+)‐ATPase with 8‐azido‐ATPEuropean Journal of Biochemistry, 1985
- Na+Na+ exchange mediated by (Na+ + K+)-ATPase reconstituted into liposomes. Evaluation of pump stoichiometry and response to ATP and ADPBiochimica et Biophysica Acta (BBA) - Biomembranes, 1985
- Occlusion of Na+ by the Na, K-ATPase in the presence of oligomycinBiochemical and Biophysical Research Communications, 1985
- Mechanism of the Na+, K+ pump protein structure and conformations of the pureBiochimica et Biophysica Acta (BBA) - Reviews on Biomembranes, 1982
- High-affinity 86Rb-binding and structural changes in the α-subunit of Na+,K+ -atpase as detected by tryptic digestion and fluorescence analysisBiochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 1982
- Occlusion of K ions in the unphosphorylated sodium pumpNature, 1979
- Manganese electron paramagnetic resonance studies of sheep kidney (sodium(1+) + potassium(1+) ion) transport adenosine triphosphatase. Interactions of substrates and activators at a single manganese(2+) ion-binding siteBiochemistry, 1979
- Lithium-7 NMR as a probe of monovalent cation sites at the active site of (Na+ + K+)-ATPase from kidneyBiochemical and Biophysical Research Communications, 1978
- Phosphorus-31 NMR studies of complexes of adenosine triphosphate, adenosine diphosphate, tripolyphosphate, and pyrophosphate with cobalt(III) amminesInorganic Chemistry, 1977
- THE ATTRACTIONS OF PROTEINS FOR SMALL MOLECULES AND IONSAnnals of the New York Academy of Sciences, 1949