Rabon E C, McFall T L, Sachs G
J Biol Chem. 1982 Jun 10;257(11):6296-9.
An H+/ATP ratio of 2 for H+ transport was determined from initial rate measurements at pH 6.1 in a purified gastric microsomal fraction containing the [H,K]ATPase. This ratio was independent of external KCl, though the apparent K0.5 for ATP was increased from 10.78 +/- 0.51 (n = 3) to 64.6 +/- 11.9 (n = 3) microM ATP and from 5.13 +/- 0.64 (n = 3) to 65.2 +/- 0.64 (n = 3) microM ATP for H+ transport and the K+-stimulated ATPase, respectively, as K+external was increased from 12 to 150 mM. The H+/ATP ratio was also relatively independent of ATP concentration. Maximum initial rates obtained in KCl-equilibrated vesicles were independent of added valinomycin, though net H+ transport was increased 29.3 +/- 1.03% (n = 6) by the addition of ionophore. Maximum net H+ transport in this vesicle preparation was 185 +/- 2.1 (n = 14) nmol mg-1 of protein. Initial rate measurements of ATPase represent a burst of K+-dependent activity of approximately 10-15 s duration. The H+/ATP stoichiometry was calculated based on the K+-stimulated component of hydrolysis. Under most conditions, the Mg2+-dependent component of hydrolysis was less than 10% of the (Mg2+ + K+) component of hydrolysis.
通过在含有[H,K]ATP酶的纯化胃微粒体组分中，于pH 6.1下进行初始速率测量，确定了H⁺转运的H⁺/ATP比率为2。尽管随着外部K⁺浓度从12 mM增加到150 mM，对于H⁺转运和K⁺刺激的ATP酶，ATP的表观K₀.₅分别从10.78±0.51（n = 3）增加到64.6±11.9（n = 3）μM ATP和从5.13±0.64（n = 3）增加到65.2±0.64（n = 3）μM ATP，但该比率与外部KCl无关。H⁺/ATP比率也相对独立于ATP浓度。在KCl平衡的囊泡中获得的最大初始速率与添加的缬氨霉素无关，尽管添加离子载体使净H⁺转运增加了29.3±1.03%（n = 6）。该囊泡制剂中的最大净H⁺转运为185±2.1（n = 14）nmol mg⁻¹蛋白质。ATP酶的初始速率测量代表了持续约10 - 15秒的K⁺依赖性活性的爆发。H⁺/ATP化学计量比是基于水解的K⁺刺激组分计算的。在大多数情况下，水解的Mg²⁺依赖性组分小于水解的（Mg²⁺ + K⁺）组分的10%。
