Department of Biochemistry and Cell Physiology, Voronezh State University, Voronezh, 394006, Russia.
Physiol Plant. 2014 Oct;152(2):231-40. doi: 10.1111/ppl.12181. Epub 2014 Apr 2.
Fumarase (EC 4.2.1.2) catalyzes reversible interconversion of malate and fumarate. It is usually associated with the tricarboxylic acid cycle in mitochondria, although the cytosolic form has also been detected. We investigated the expression of two fumarase genes and activities of the mitochondrial and cytosolic isoforms of fumarase in maize (Zea mays) scutellum during germination. Both isoforms were purified to electrophoretic homogeneity. The cytosolic form had low optimum pH (6.5) and high affinity to malate (Km 5 μM) when compared with the mitochondrial form (optimum pH 7.0, Km 50 μM). The cytosolic form was strongly activated by Mg(2+) and even more by Mn(2+) , whereas the mitochondrial form was moderately activated by Mg(2+) and Mn(2+) was less effective. The highest fumarase activity in scutellum and a high expression of the gene encoding the cytosolic form were observed during the maximal activity of the glyoxylate cycle. In leaves, the localization of fumarase is only mitochondrial and only one fumarase gene is expressed. It is concluded that the function of cytosolic fumarase in maize scutellum can be related to metabolism of succinate formed in the glyoxylate cycle.
延胡索酸酶（EC 4.2.1.2）催化苹果酸和延胡索酸的可逆转化。它通常与线粒体中的三羧酸循环相关联，尽管也检测到了胞质形式。我们研究了玉米（Zea mays）盾片中两种延胡索酸酶基因的表达以及延胡索酸酶的线粒体和胞质同工酶的活性。两种同工酶均被纯化至电泳均一性。与线粒体形式（最适 pH 7.0，Km 50 μM）相比，胞质形式的最适 pH 较低（6.5），对苹果酸的亲和力较高（Km 5 μM）。与线粒体形式相比，胞质形式被 Mg2+强烈激活，甚至 Mn2+更能激活，而线粒体形式被 Mg2+适度激活，Mn2+的效果较差。在乙醛酸循环的最大活性期间，盾片中的延胡索酸酶活性最高，并且编码胞质形式的基因表达水平最高。在叶片中，延胡索酸酶的定位仅为线粒体，并且仅表达一个延胡索酸酶基因。因此，可以得出结论，玉米盾片中胞质延胡索酸酶的功能可能与乙醛酸循环中形成的琥珀酸的代谢有关。
