title: Changes in affinity of Na+- and K+-transport ATPase for divalent cations during its reaction sequence.
abstract: Previous experiments (Fukushima, Y., and Post, R.L. (1978) J. Biol. Chem. 253, 6853-6862) demonstrated that the Ca x phosphoenzyme of sodium- and potassium-transport adenosine triphosphatase gradually becomes stable after dissociation of Ca2+ in the presence of a chelating agent such as 1,2-cyclohexylenedinitrilo-tetraacetic acid. In the present study, we investigated whether the ADP- and K+-sensitive forms of the Ca x phosphoenzyme show different affinities for divalent cations. Our findings were as follows. (a) As the concentraion of Na+ was increased during phosphorylation of the enzyme with ATP at pH 7.4 and 0 degrees C, both the sensitivity to ADP and the amount of calcium-free phosphoenzyme increased in parallel. (b) For this Na+-dependent change, kidney enzyme required higher concentrations of Na+ than did brain enzyme. (c) In addition, the rate of dissociation of Ca2+ from the ADP-sensitive Ca x phosphoenzyme was faster than that from the K+-sensitive phosphoenzyme. It was thus concluded that Ca2+ binds to the ADP-sensitive phosphoenzyme less tightly than to the K+-sensitive phosphoenzyme.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D004492:Edetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D007668:Kidney / Q000201:enzymology; D008274:Magnesium / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
chemical_list: D002413:Cations, Divalent; D002614:Chelating Agents; D003035:Cobalt; C005390:CDTA; D000244:Adenosine Diphosphate; D004492:Edetic Acid; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D002118:Calcium