Hara Y, Yamada J, Nakao M
J Biochem. 1986 Feb;99(2):531-9. doi: 10.1093/oxfordjournals.jbchem.a135509.
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+.
研究了H⁺可能在Na⁺,K⁺-ATP酶的Na⁺位点替代Na⁺的可能性。从猪肾中纯化的Na⁺,K⁺-ATP酶在酸性pH值（H⁺,K⁺-ATP酶）且无Na⁺的情况下表现出对哇巴因敏感的K⁺依赖性ATP酶活性。在pH 5.7时比活性为1.1 μmol Pi/mg/min，而在pH 7.5时Na⁺,K⁺-ATP酶的比活性为14 μmol Pi/mg/min。该酶在酸性pH值且无Na⁺的情况下可从ATP进行磷酸化。在酸性pH值且无Na⁺时，磷酸化的初始速率也加快，在pH 5.5且无Na⁺时获得的最大速率是在pH 7.0且有Na⁺时速率的9%。磷酶对K⁺敏感但对ADP几乎不敏感。磷酶对羟胺处理敏感，并且发现该酶的α亚基被磷酸化。H⁺,K⁺-ATP酶与Na⁺,K⁺-ATP酶一样有效地被N-乙基马来酰胺抑制，但受寡霉素或二甲基亚砜的抑制较小。这些结果表明质子对Na⁺,K⁺-ATP酶的Na⁺位点具有类似Na⁺的作用，并表明质子可以通过钠泵代替Na⁺进行转运。
