Guranowski A, Blanquet S
J Biol Chem. 1985 Mar 25;260(6):3542-7.
Novel enzymatic activity which splits diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) phosphorolytically has been found in extracts from Saccharomyces cerevisiae. One of the two alpha,beta-anhydride bonds between Ap4A phosphate residues undergoes phosphorolysis, and ATP (pppA) plus ADP (ppA) are the products of the reaction according to the equation: AppppA + Pi----pppA + ppA The reaction is dependent on the presence of divalent metal ions; Mn2+ or Mg2+ sustain the greatest rates of reaction. Among analogues of the Ap4A substrate, Ap5A and Gp4G, but not p4A and Ap3A, are substrates, and corresponding products are p4A plus ADP, and GTP plus GDP, the phosphate being incorporated into the nucleoside 5'-diphosphates. In the reactions, phosphate can be substituted with arsenate. Arsenolysis of Ap4A, Ap5A, or Gp4G leads to ATP plus AMP, p4A plus AMP, and GTP plus GMP, respectively. The name diadenosine tetraphosphate alpha,beta-phosphorylase (ADP-forming) is proposed for the new enzyme. The phosphorylase has been purified to apparent homogeneity and behaves as a single polypeptide chain of Mr = 40,000. Optimum activity of the enzyme is at pH 8.0 and the sulfhydryl groups are essential for catalysis. At saturating Ap4A, the rate constant for the reaction is 36 s-1 and the Km value for Ap4A is 60 microM (37 degrees C, 50 mM Hepes/KOH (pH 8.2), 500 microM MnCl2, 10 mM K2HPO4, 1 mM 2-mercaptoethanol, and 2% glycerol). The Km values for phosphate and arsenate are 1 and 3 mM, respectively.
在酿酒酵母提取物中发现了一种新型酶活性，该活性可磷酸解二腺苷5',5'''-P1,P4-四磷酸（Ap4A）。Ap4A磷酸残基之间的两个α,β-酸酐键之一发生磷酸解，根据以下方程式，ATP（pppA）和ADP（ppA）是反应产物：AppppA + Pi----pppA + ppA 该反应依赖于二价金属离子的存在；Mn2+或Mg2+能维持最大反应速率。在Ap4A底物类似物中，Ap5A和Gp4G是底物，而p4A和Ap3A不是，相应产物分别是p4A加ADP以及GTP加GDP，磷酸被掺入核苷5'-二磷酸中。在反应中，磷酸盐可用砷酸盐替代。Ap4A、Ap5A或Gp4G的砷解分别导致ATP加AMP、p4A加AMP以及GTP加GMP。建议将这种新酶命名为二腺苷四磷酸α,β-磷酸化酶（形成ADP）。该磷酸化酶已纯化至表观均一，表现为一条Mr = 40,000的单多肽链。该酶的最佳活性在pH 8.0，巯基对于催化至关重要。在Ap4A饱和时，反应速率常数为36 s-1，Ap4A的Km值为60 μM（37℃，50 mM Hepes/KOH（pH 8.2），500 μM MnCl2，10 mM K2HPO4，1 mM 2-巯基乙醇和2%甘油）。磷酸盐和砷酸盐的Km值分别为1 mM和3 mM。
