Sodium acts as a potassium analog on gastric H,K-ATPase.
The effects of Na+ on gastric H,K-ATPase were investigated using leaky and ion-tight H,K-ATPase vesicles. Na+ activated the total ATPase activity in the absence of K+, reaching levels of 15% relative to those in the presence of K+. The Na+ activation, which takes place at the luminal side of the membrane, depended on the ATP concentration and the type of buffer used. The steady-state ATP phosphorylation level, studied with leaky vesicles, was reduced by Na+ due to both activation of the dephosphorylation reaction and a shift to E2 in the E1<==>E2 equilibrium. By studying this equilibrium in ion-tight H,K-ATPase vesicles, it was found that Na+ drives the enzyme via a cytosolic site to the nonphosphorylating E2 conformation. No H(+)-like properties of cytosolic Na+ could be detected. We therefore conclude that Na+ behaves like K+ rather than like H+ in the H,K-ATPase reaction.
Swarts
H G
HG
Department of Biochemistry, University of Nijmegen, The Netherlands.
Klaassen
C H
CH
Schuurmans Stekhoven
F M
FM
De Pont
J J
JJ
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004789:Enzyme Activation; D017506:H(+)-K(+)-Exchanging ATPase / Q000187:drug effects* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010766:Phosphorylation; D011188:Potassium / Q000737:chemistry / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology*; D013270:Stomach / Q000201:enzymology*; D013552:Swine
D007093:Imidazoles; C035235:Sch 28080; D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium