Although the capacity of isolated beta-subunits of the ATP synthase/ATPase to perform catalysis has been extensively studied, the results have not conclusively shown that the subunits are catalytically active. Since soluble F(1) of mitochondrial H(+)-ATPase can bind inorganic pyrophosphate (PP(i)) and synthesize PP(i) from medium phosphate, we examined if purified His-tagged beta-subunits from Thermophilic bacillus PS3 can hydrolyze PP(i). The difference spectra in the near UV CD of beta-subunits with and without PP(i) show that PP(i) binds to the subunits. Other studies show that beta-subunits hydrolyze [(32)P] PP(i) through a Mg(2+)-dependent process with an optimal pH of 8.3. Free Mg(2+) is required for maximal hydrolytic rates. The Km for PP(i) is 75 microM and the Vmax is 800 pmol/min/mg. ATP is a weak inhibitor of the reaction, it diminishes the Vmax and increases the Km for PP(i). Thus, isolated beta-subunits are catalytically competent with PP(i) as substrate; apparently, the assembly of beta-subunits into the ATPase complex changes substrate specificity, and leads to an increase in catalytic rates.

中文翻译：

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来自嗜热芽孢杆菌 PS3 的 ATP 合酶/ATP 酶的分离的 β 亚基催化。焦磷酸盐的水解。

尽管已对 ATP 合酶/ATP 酶的分离的 β 亚基进行催化的能力进行了广泛研究，但结果并未最终表明这些亚基具有催化活性。由于线粒体 H(+)-ATPase 的可溶性 F(1) 可以结合无机焦磷酸盐 (PP(i)) 并从中等磷酸盐中合成 PP(i)，我们检查了来自嗜热杆菌 PS3 的纯化 His 标记的β-亚基是否可以水解PP(i)。带有和不带有 PP(i) 的 β 亚基的近紫外 CD 中的差异光谱表明 PP(i) 与亚基结合。其他研究表明，β 亚基通过 Mg(2+) 依赖过程水解 [(32)P] PP(i)，最佳 pH 值为 8.3。最大水解速率需要游离 Mg(2+)。PP(i) 的 Km 为 75 microM，Vmax 为 800 pmol/min/mg。ATP 是反应的弱抑制剂，它减少了 Vmax 并增加了 PP(i) 的 Km。因此，分离的 β 亚基与作为底物的 PP(i) 具有催化能力；显然，将 β 亚基组装到 ATP 酶复合物中会改变底物特异性，并导致催化速率增加。