REVERSIBLE DISSOCIATION OF THE CATALYTICALLY ACTIVE SUBUNITS OF PIGEON LIVER MALIC ENZYME
REVERSIBLE DISSOCIATION OF THE CATALYTICALLY ACTIVE SUBUNITS OF PIGEON LIVER MALIC ENZYME
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DOI：
10.1042/bj2540123
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发表时间：
1988-08-15
影响因子：
4.1
通讯作者：
CHANG, TC
中科院分区：
文献类型：
--
作者：
CHANG, GG;HUANG, TM;CHANG, TC
采用化学交联和SDS/聚丙烯酰胺凝胶电泳相结合的方法，研究了鸽肝苹果酸酶（EC 1.1.1.40）在pH诱导下的可逆解离。四聚体酶在酸性环境中表现出pH依赖性解离。在pH值高于8.0时，大多数分子以四聚体形式存在。酶在较低的pH值下逐渐解离。当pH值高于5.0时，大部分酶以单体形式存在。通过将pH调节至中性来完成亚基的重新缔合。分离和重新结合几乎是瞬间的。未检测到三聚体。因此，鸽子肝苹果酸酶被证明具有D2对称性的双二聚体四级结构。在底物的存在下，单体-二聚体-四聚体平衡有利于解离的方向。柠檬酸盐，一种L-苹果酸类似物，被发现在这个过程中比L-苹果酸更有效。当单体形式被固定化时，发现酶亚基在催化中具有完全活性。一个可能的安排的四个相同的亚基的酶分子的建议，以解释在这项调查中获得的结果。本文还对鸽肝苹果酸酶半位点反应性的起源进行了讨论。
The pH-induced reversible dissociation of pigeon liver malic enzyme (EC 1.1.1.40) was studied by combined use of chemical cross-linking and SDS/polyacrylamide-gel electrophoresis. The tetrameric enzyme showed at pH-dependent dissociation in an acidic environment. At pH values above 8.0 most molecules existed as tetramers. The enzyme was gradually dissociated at lower pH. When the pH was above 5.0 most of the enzyme was present as the monomeric forms. Reassociation of the subunits was accomplished by adjusting the pH to neutrality. The dissociation and reassociation were almost instantaneous. No trimer was detected. The pigeon liver malic enzyme was thus shown to have a double-dimer quaternary structure with D2 symmetry. In the presence of substrates, the monomer-dimer-tetramer equilibrium favours the direction of dissociation. Tartronate, an L-malate analogue, was found to be more effective than L-malate in this process. When the monomeric forms were immobilized, the enzyme subunits were found to be fully active in catalysis. A possible arrangement of the four identical subunits of the enzyme molecule is proposed to account for the results obtained in this investigation. The origin of the half-of-the-sites reactivity of pigeon liver malic enzyme is also discussed.