La Cognata U, Landschütze V, Willmitzer L, Müller-Röber B
Institut für Genbiologische Forschung Berlin GmbH (IGF), Germany.
Plant Cell Physiol. 1996 Oct;37(7):1022-9. doi: 10.1093/oxfordjournals.pcp.a029033.
Mitochondrial citrate synthase (EC 4.1.3.7) represents the first enzyme of the tricarboxylic acid cycle, catalyzing the condensation of acetyl-CoA and oxaloacetate, finally yielding citrate and CoA. We report here the isolation of cDNA clones encoding citrate synthase from Nicotiana tabacum, Beta vulgaris and Populus. Nucleotide and deduced amino acid sequences were compared with previously published sequences of mitochondrial citrate synthases from Arabidopsis thaliana and potato, as well as with the sequence of glyoxysomal citrate synthase from pumpkin. Homologies between the various plant mitochondrial enzymes were in the range from 77.2% (potato vs. Arabidopsis) to 94.2% (potato vs. tobacco) on the nucleotide level (coding regions only), and in the range from 70.1% to 90.4% (potato vs. Arabidopsis, and potato vs. tobacco, respectively) on the amino acid level. Identities of the mitochondrial isozymes to the pumpkin glyoxysomal enzyme were below 30% on the nucleotide and amino acid level. In Northern blot experiments citrate synthase mRNA was detected in all tissues analyzed. However, levels of expression showed tissue dependency despite the fact that citrate synthase is usually considered a house-keeping enzyme. Whether these different levels of expression reflect tissue-specific variations with respect to basic metabolism awaits further analysis.
线粒体柠檬酸合酶（EC 4.1.3.7）是三羧酸循环的首个酶，催化乙酰辅酶A和草酰乙酸的缩合反应，最终生成柠檬酸和辅酶A。我们在此报告从烟草、甜菜和杨树中分离出编码柠檬酸合酶的cDNA克隆。将核苷酸序列和推导的氨基酸序列与先前发表的拟南芥和马铃薯线粒体柠檬酸合酶序列，以及南瓜乙醛酸循环体柠檬酸合酶序列进行了比较。仅在编码区的核苷酸水平上，各种植物线粒体酶之间的同源性在77.2%（马铃薯与拟南芥）至94.2%（马铃薯与烟草）之间；在氨基酸水平上，同源性在70.1%至90.4%之间（分别为马铃薯与拟南芥、马铃薯与烟草）。线粒体同工酶与南瓜乙醛酸循环体酶在核苷酸和氨基酸水平上的同一性均低于30%。在Northern杂交实验中，在所分析的所有组织中均检测到了柠檬酸合酶mRNA。然而，尽管柠檬酸合酶通常被认为是一种持家酶，但其表达水平仍表现出组织依赖性。这些不同的表达水平是否反映了基础代谢方面的组织特异性差异，还有待进一步分析。
