ADP刺激钠钾ATP酶和钙ATP酶中“ADP不敏感”磷酸酶的水解。

ADP stimulates hydrolysis of the "ADP-insensitive" phosphoenzyme in Na+, K+-ATPase and Ca2+-ATPase.

作者信息

Hobbs A S, Albers R W, Froehlich J P, Heller P F

出版信息

J Biol Chem. 1985 Feb 25;260(4):2035-7.

Abstract

ADP-sensitive (E1P) and K+-sensitive (E2P) phosphoenzymes are sequentially formed intermediates in the reaction pathways catalyzed by the Na+,K+- and Ca2+-ATPases. The kinetics of dephosphorylation of these intermediates were examined by means of rapid quenching with acid at 21 degrees C. Under conditions favoring the formation of E2P (25 mM Na+ and O K+), addition of 5 mM ADP + 10 mM EDTA to the Na+,K+-ATPase phosphoenzyme produced a biphasic pattern of dephosphorylation. Both phases of phosphoenzyme decomposition were accompanied by approximately stoichiometric amounts of inorganic phosphate (Pi) release. The rate of decay of the rapid phase was 10 times faster than the rate of phosphoenzyme turnover under phosphorylating conditions indicating acceleration of E2P hydrolysis by ADP. Similar patterns of ADP-stimulated phosphoenzyme decay and Pi release were observed in the Ca2+-ATPase from sarcoplasmic reticulum phosphorylated at low (0.1 mM) Mg2+ in the absence of KCl. These results demonstrate that ADP can enhance the rate of E2P hydrolysis in the cases of the Na+,K+-ATPase and Ca2+-ATPase. As a consequence measurement of "ADP-sensitive EP" may overestimate E1P.

摘要

ADP敏感型（E1P）和K⁺敏感型（E2P）磷酸酶是由Na⁺,K⁺ - ATP酶和Ca²⁺ - ATP酶催化的反应途径中的顺序形成中间体。在21℃下通过酸快速淬灭来研究这些中间体的去磷酸化动力学。在有利于E2P形成的条件下（25 mM Na⁺和0 K⁺），向Na⁺,K⁺ - ATP酶磷酸酶中加入5 mM ADP + 10 mM EDTA会产生双相去磷酸化模式。磷酸酶分解的两个阶段都伴随着近似化学计量的无机磷酸盐（Pi）释放。快速阶段的衰减速率比磷酸化条件下磷酸酶周转速率快10倍，表明ADP加速了E2P水解。在无KCl的情况下，在低（0.1 mM）Mg²⁺条件下磷酸化的肌浆网Ca²⁺ - ATP酶中观察到类似的ADP刺激的磷酸酶衰减和Pi释放模式。这些结果表明，在Na⁺,K⁺ - ATP酶和Ca²⁺ - ATP酶的情况下，ADP可以提高E2P水解的速率。因此，“ADP敏感型EP”的测量可能会高估E1P。