L-Threonine dehydrogenase of chicken liver. Purification, characterization, and physiological significance.
L-Threonine dehydrogenase of chicken liver. Purification, characterization, and physiological significance.
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DOI：
10.1016/s0021-9258(18)43281-4
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发表时间：
1981-12
期刊：
影响因子：
--
通讯作者：
Y. Aoyama;Y. Motokawa
中科院分区：
文献类型：
--
作者：
Y. Aoyama;Y. Motokawa
从鸡肝线粒体中纯化出l -苏氨酸脱氢酶（l -苏氨酸：NAD+氧化还原酶，EC 1.1.1.103），具有明显的同质性。在纯化和储存过程中，2-巯基乙醇和甘油的存在是稳定酶的必要条件。酶是一个单体，其Mr大约等于88,000。酶的最适pH为8.6 ~ 8.7，酶的等电点为5.9。这种酶对l -苏氨酸和NAD+有特异性。l -苏氨酸和NAD+的Km值分别为8.4和0.98 mM。动力学研究表明，NAD+先加入，l -苏氨酸后加入，为有序毕比反应机制。鸡肝线粒体含有氨基丙酮合成酶（acetyl-CoA:glycine C-acetyltransferase (EC 2.3.1.29)）。这种酶已被部分纯化。在l-苏氨酸脱氢酶和氨基丙酮合成酶存在下，l-苏氨酸通过2-氨基-3-氧丁酸酯裂解为甘氨酸和乙酰辅酶a。提示l -苏氨酸脱氢酶和氨基丙酮合成酶在脊椎动物l -苏氨酸代谢中具有生理作用。
L-Threonine dehydrogenase (L-threonine:NAD+ oxidoreductase (EC 1.1.1.103) has been purified to apparent homogeneity from chicken liver mitochondria. The presence of 2-mercaptoethanol and glycerol is necessary for stabilizing the enzyme during purification and storage. The enzyme is a monomer and has Mr approximately equal to 88,000. The pH optimum is 8.6 to 8.7, and the isoelectric point of the enzyme is 5.9. The enzyme is specific for L-threonine and NAD+. The Km values for L-threonine and NAD+ are 8.4 and 0.98 mM, respectively. Kinetic studies indicate that the reaction proceeds through an Ordered Bi Bi mechanism where NAD+ is added first, followed by L-threonine. Chicken liver mitochondria contain aminoacetone synthase (acetyl-CoA:glycine C-acetyltransferase (EC 2.3.1.29)). The enzyme has been partially purified. In the presence of L-threonine dehydrogenase and aminoacetone synthase, L-threonine is cleaved to glycine and acetyl-CoA via 2-amino-3-oxobutyrate. The result suggests that L-threonine dehydrogenase and aminoacetone synthase have a physiological role in L-threonine metabolism in vertebrates.