Stengelin M, Fendler K, Bamberg E
Max-Planck-Institut für Biophysik, Frankfurt am Main, FRG.
J Membr Biol. 1993 Mar;132(3):211-27. doi: 10.1007/BF00235739.
(H,K)-ATPase containing membranes from hog stomach were attached to black lipid membranes. Currents induced by an ATP concentration jump were recorded and analyzed. A sum of three exponentials (tau 1(-1) approximately 400 sec-1, tau 2(-1) approximately 100 sec-1, tau 3(-1) approximately 10 sec-1; T = 300 K, pH 6, MgCl2 3 mM, no K+) was fitted to the transient signal. The dependence of the resulting time constants and the peak current on electrolyte composition, ATP conversion rate, temperature, and membrane conductivity was recorded. The results are consistent with a reaction scheme similar to that proposed by Albers and Post for the NaK-ATPase. Based on this model the following assignments were made: tau 2 corresponds to ATP binding and exchange with caged ATP. tau 1 describes the phosphorylation reaction E1 x ATP-->E1P. The third, slowest time constant tau 3 is tentatively assigned to the E1P-->E2P transition. This is the first electrogenic step and is accelerated at high pH and by ATP via a low affinity binding site. The second electrogenic step is the transition from E2K to E1H. The E2K<==>E1H equilibrium is influenced by potassium with an apparent K0.5 of 3 mM and by the pH. Low pH and low potassium concentration stabilize the E1 conformation.
将来自猪胃的含（H，K）-ATP酶的膜附着于黑色脂质膜上。记录并分析由ATP浓度跃变诱导的电流。用三个指数之和（τ1（-1）约为400秒-1，τ2（-1）约为100秒-1，τ3（-1）约为10秒-1；T = 300 K，pH 6，MgCl2 3 mM，无K+）拟合瞬态信号。记录了所得时间常数和峰值电流对电解质组成、ATP转化率、温度和膜电导率的依赖性。结果与Albers和Post提出的NaK-ATP酶反应方案相似。基于该模型进行了以下赋值：τ2对应于ATP结合以及与笼形ATP的交换。τ1描述磷酸化反应E1×ATP→E1P。第三个也是最慢的时间常数τ3暂时指定为E1P→E2P转变。这是第一个电生步骤，在高pH值下以及通过低亲和力结合位点的ATP会加速该步骤。第二个电生步骤是从E2K到E1H的转变。E2K⇌E1H平衡受钾（表观K0.5为3 mM）和pH值的影响。低pH值和低钾浓度会稳定E1构象。
