Hara Y, Nakao M
J Biochem. 1981 Oct;90(4):923-31. doi: 10.1093/oxfordjournals.jbchem.a133580.
The two phosphoenzymes (E1P and E2P) of Na+,K+-ATPase were measured as ADP-sensitive and K+-sensitive fractions. The sum of these fractions was nearly 1 in the range of 50 to 1,200 mM NaCl. The effects of Na+ on the levels of E1P and E2P, on the rate constant of E2P leads to E1P transition (k2), on the rate constant of E2P dephosphorylation (k3), on the rate constant of E1P leads to E2P transition (k1) and on the apparent equilibrium constant between E1P and E2P (Kapp) were examined. k1 was found to decrease with increasing Na+ concentration, whereas k2 increased. Kapp was found to be directly proportional to the third power of Na+ concentration. k3 increased with increasing Na+ concentration and saturated at about 1 M NaCl. These results are consistent with a simple model in which ATP hydrolysis occurs through effectively only two phosphoenzyme intermediates in the absence of K+ and three sodium ions are discharged cooperatively from the enzyme during the E1P leads to E2P conversion.
钠钾ATP酶的两种磷酸化酶（E1P和E2P）被测定为ADP敏感和钾敏感部分。在50至1200 mM NaCl范围内，这些部分的总和接近1。研究了钠离子对E1P和E2P水平、E2P向E1P转变的速率常数（k2）、E2P去磷酸化的速率常数（k3）、E1P向E2P转变的速率常数（k1）以及E1P和E2P之间的表观平衡常数（Kapp）的影响。发现k1随着钠离子浓度的增加而降低，而k2增加。发现Kapp与钠离子浓度的三次方成正比。k3随着钠离子浓度的增加而增加，并在约1 M NaCl时达到饱和。这些结果与一个简单模型一致，即在没有钾离子的情况下，ATP水解仅通过两种有效的磷酸化酶中间体发生，并且在E1P向E2P转化过程中，三个钠离子协同从酶中排出。
