title: Existence of ADP- and KCl-insensitive phosphoenzyme intermediate of Na+,K(+)-ATPase at alkaline Ph.
abstract: The Na(+)-ATPase activity of Na+,K(+)-ATPase in the absence of K+ was least dependent on the sodium concentration when the pH was 9.5. Around 40% of the phosphoenzyme formed from ATP in the presence of 0.5 mM MgCl2 at alkaline pH was insensitive to both KCl and ADP. High-Na+ chase reversed this insensitivity, i.e., the phosphoenzyme became sensitive to KCl or ADP. On the other hand, phosphorylation at 0.1 mM MgCl2 instead of 0.5 mM showed at least 95% sensitivity to KCl. These observations suggest that ADP- and KCl-insensitive phosphoenzyme was formed when excess Mg++ was present during phosphorylation at alkaline pH. This phosphoenzyme might be an intermediate in the process of ATP hydrolysis.
authors.affiliation: Department of Biochemistry, Tokyo Medical and Dental University School of Medicine, Japan.
authors.forename: R R
authors.initials: RR
authors.lastname: Siagian
authors.forename: Y
authors.initials: Y
authors.lastname: Hara
authors.forename: M
authors.initials: M
authors.lastname: Nakao
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D015636:Magnesium Chloride / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation; D011189:Potassium Chloride / Q000378:metabolism / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
chemical_list: D015636:Magnesium Chloride; D000244:Adenosine Diphosphate; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase