Paoli P, Camici G, Manao G, Giannoni E, Ramponi G
Dipartimento di Scienze Biochimiche, Università di Firenze, Viale Morgagni 50, 50134 Firenze, Italy.
Biochem J. 2000 Jul 1;349(Pt 1):43-9. doi: 10.1042/0264-6021:3490043.
We have demonstrated that acylphosphatase possesses ATP-diphosphohydrolase (apyrase-like) activity. In fact, acylphosphatase first catalyses the hydrolysis of the gamma-phosphate group of nucleoside triphosphates, and then attacks the beta-phosphate group of the initially produced nucleoside diphosphates, generating nucleoside monophosphates. In contrast, it binds nucleoside monophosphates but does not catalyse their hydrolyses. The calculated k(cat) values for the nucleoside triphosphatase activity of acylphosphatase are of the same order of magnitude as those displayed by certain G-proteins. An acidic environment enhances the apyrase-like activity of acylphosphatase. The true nucleotide substrates of acylphosphatase are free nucleoside di- and triphosphates, as indicated by the Mg(2+) ion inhibition of the activity. We have also demonstrated that, although nucleoside triphosphates are still hydrolysed at pH 7.2 and 37 degrees C, in the presence of millimolar Mg(2+) concentrations this occurs at a lower rate. Taken together with the previously observed strong increase of acylphosphatase levels during induced cell differentiation, our findings suggest that acylphosphatase plays an active role in the differentiation process (as well as in other processes, such as apoptosis) by modulating the ratio between the cellular levels of nucleoside diphosphates and nucleoside triphosphates.
我们已经证明酰基磷酸酶具有ATP - 二磷酸水解酶（类腺苷三磷酸双磷酸酶）活性。事实上，酰基磷酸酶首先催化核苷三磷酸的γ - 磷酸基团水解，然后作用于最初生成的核苷二磷酸的β - 磷酸基团，生成核苷单磷酸。相反，它能结合核苷单磷酸但不催化其水解。酰基磷酸酶核苷三磷酸酶活性的计算催化常数（k(cat)）值与某些G蛋白所显示的值处于同一数量级。酸性环境会增强酰基磷酸酶的类腺苷三磷酸双磷酸酶活性。如Mg(2+)离子对活性的抑制所示，酰基磷酸酶真正的核苷酸底物是游离的核苷二磷酸和核苷三磷酸。我们还证明，尽管在pH 7.2和37摄氏度时核苷三磷酸仍会水解，但在存在毫摩尔浓度的Mg(2+)时，水解速率较低。结合之前在诱导细胞分化过程中观察到的酰基磷酸酶水平的强烈增加，我们的研究结果表明，酰基磷酸酶通过调节细胞内核苷二磷酸和核苷三磷酸水平的比例，在分化过程（以及其他过程，如细胞凋亡）中发挥积极作用。
