Proton transport catalyzed by the sodium pump. Ouabain-sensitive ATPase activity and the phosphorylation of Na,K-ATPase in the absence of sodium ions.
The possibility that H+ might substitute for Na+ at Na+ sites of Na+,K+-ATPase was studied. Na+,K+-ATPase purified from pig kidney showed ouabain-sensitive K+-dependent ATPase activity in the absence of Na+ at acid pH (H+,K+-ATPase). The specific activity was 1.1 mumol Pi/mg/min at pH 5.7, whereas the specific activity of Na+,K+-ATPase was 14 mumol Pi/mg/min at pH 7.5. The enzyme was phosphorylated from ATP in the absence of Na+ at the acid pH. The initial rate of the phosphorylation was also accelerated at the acid pH in the absence of Na+, and the maximal rate obtained at pH 5.5 without Na+ was 9% of the rate at pH 7.0 with Na+. The phosphoenzyme was sensitive to K+ but almost insensitive to ADP. The phosphoenzyme was sensitive to hydroxylamine treatment and the alpha-subunit of the enzyme was found to be phosphorylated. H+,K+-ATPase was inhibited as effectively as Na+,K+-ATPase by N-ethylmaleimide but was less inhibited by oligomycin or dimethyl sulfoxide. These results indicate that protons have an Na+-like effect on the Na+ sites of Na+,K+-ATPase and suggest that protons can be transported by the sodium pump in place of Na+.
Hara
Y
Y
Yamada
J
J
Nakao
M
M
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D002021:Buffers; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D007679:Kidney Medulla / Q000201:enzymology; D010042:Ouabain / Q000494:pharmacology; D010766:Phosphorylation; D011522:Protons; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
D002021:Buffers; D007473:Ion Channels; D011522:Protons; D010042:Ouabain; D012964:Sodium; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase