Falzone C J, Karsten W E, Conley J D, Viola R E
Department of Chemistry, University of Akron, Ohio 44325.
Biochemistry. 1988 Dec 27;27(26):9089-93. doi: 10.1021/bi00426a004.
The enzyme L-aspartase from Escherichia coli has an absolute specificity for its amino acid substrate. An examination of a wide range of structural analogues of L-aspartic acid did not uncover any alternate substrates for this enzyme. A large number of competitive inhibitors of the enzyme have been characterized, with inhibition constants ranging over 2 orders of magnitude. A divalent metal ion is required for enzyme activity above pH 7, and this requirement is met by many transition and alkali earth metals. The binding stoichiometry has been established to be one metal ion bound per subunit. Paramagnetic relaxation studies have shown that the divalent metal ion binds at the recently discovered activator site on L-aspartase and not at the enzyme active site. Enzyme activators are bound within 5 A of the enzyme-bound divalent metal ion. The activator site is remote from the active site of the enzyme, since the relaxation of inhibitors that bind at the active site is not affected by paramagnetic metal ions bound at the activator site.
来自大肠杆菌的L-天冬氨酸酶对其氨基酸底物具有绝对特异性。对多种L-天冬氨酸结构类似物的研究未发现该酶的任何替代底物。已对该酶的大量竞争性抑制剂进行了表征，其抑制常数范围超过2个数量级。在pH 7以上的酶活性需要二价金属离子，许多过渡金属和碱土金属可满足这一需求。已确定结合化学计量为每个亚基结合一个金属离子。顺磁弛豫研究表明，二价金属离子结合在L-天冬氨酸酶最近发现的激活位点，而不是酶活性位点。酶激活剂结合在与酶结合的二价金属离子5埃范围内。激活位点远离酶的活性位点，因为在活性位点结合的抑制剂的弛豫不受在激活位点结合的顺磁金属离子的影响。
