Caruso-Neves C, Coelho-Souza S A, Vives D, Goes G, Lara L S, Lopes A G
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, CCS Bloco G, 21949 Rio de Janeiro (RJ), Brazil.
Int J Biochem Cell Biol. 2002 Dec;34(12):1586-93. doi: 10.1016/s1357-2725(02)00059-6.
In addition to the (Na(+)+K(+))ATPase another P-ATPase, the ouabain-insensitive Na(+)-ATPase has been observed in several tissues. In the present paper, the effects of ligands, such as Mg(2+), MgATP and furosemide on the Na(+)-ATPase and its modulation by pH were studied in the proximal renal tubule of pig. The principal kinetics parameters of the Na(+)-ATPase at pH 7.0 are: (a) K(0.5) for Na(+)=8.9+/-2.2mM; (b) K(0.5) for MgATP=1.8+/-0.4mM; (c) two sites for free Mg(2+): one stimulatory (K(0.5)=0.20+/-0.06 mM) and other inhibitory (I(0.5)=1.1+/-0.4 mM); and (d) I(0.5) for furosemide=1.1+/-0.2 mM. Acidification of the reaction medium to pH 6.2 decreases the apparent affinity for Na(+) (K(0.5)=19.5+/-0.4) and MgATP (K(0.5)=3.4+/-0.3 mM) but increases the apparent affinity for furosemide (0.18+/-0.02 mM) and Mg(2+) (0.05+/-0.02 mM). Alkalization of the reaction medium to pH 7.8 decreases the apparent affinity for Na(+) (K(0.5)=18.7+/-1.5 mM) and furosemide (I(0.5)=3.04+/-0.57 mM) but does not change the apparent affinity to MgATP and Mg(2+). The data presented in this paper indicate that the modulation of the Na(+)-ATPase by pH is the result of different modifications in several steps of its catalytical cycle. Furthermore, they suggest that changes in the concentration of natural ligands such as Mg(2+) and MgATP complex may play an important role in the Na(+)-ATPase physiological regulatory mechanisms.
除了（Na⁺ + K⁺）ATP 酶外，另一种 P - ATP 酶，即哇巴因不敏感的 Na⁺ - ATP 酶已在多种组织中被观察到。在本文中，研究了诸如 Mg²⁺、MgATP 和呋塞米等配体对猪近端肾小管中 Na⁺ - ATP 酶的影响及其受 pH 的调节作用。在 pH 7.0 时，Na⁺ - ATP 酶的主要动力学参数如下：（a）Na⁺的半饱和常数（K₀.₅）= 8.9 ± 2.2 mM；（b）MgATP 的半饱和常数（K₀.₅）= 1.8 ± 0.4 mM；（c）游离 Mg²⁺的两个位点：一个起刺激作用（K₀.₅ = 0.20 ± 0.06 mM），另一个起抑制作用（抑制常数 I₀.₅ = 1.1 ± 0.4 mM）；（d）呋塞米的抑制常数（I₀.₅）= 1.1 ± 0.2 mM。将反应介质酸化至 pH 6.2 会降低对 Na⁺（K₀.₅ = 19.5 ± 0.4）和 MgATP（K₀.₅ = 3.4 ± 0.3 mM）的表观亲和力，但会增加对呋塞米（0.18 ± 0.02 mM）和 Mg²⁺（0.05 ± 0.02 mM）的表观亲和力。将反应介质碱化至 pH 7.8 会降低对 Na⁺（K₀.₅ = 18.7 ± 1.5 mM）和呋塞米（I₀.₅ = 3.04 ± 0.57 mM）的表观亲和力，但不会改变对 MgATP 和 Mg²⁺的表观亲和力。本文所呈现的数据表明，pH 对 Na⁺ - ATP 酶的调节是其催化循环多个步骤中不同修饰的结果。此外，它们表明诸如 Mg²⁺和 MgATP 复合物等天然配体浓度的变化可能在 Na⁺ - ATP 酶的生理调节机制中起重要作用。
