Mitsch M J, Voegele R T, Cowie A, Osteras M, Finan T M
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
J Biol Chem. 1998 Apr 10;273(15):9330-6. doi: 10.1074/jbc.273.15.9330.
Malic enzymes catalyze the oxidative decarboxylation of malate to pyruvate in conjunction with the reduction of a nicotinamide cofactor. We determined the DNA sequence and transcriptional start sites of the genes encoding the diphosphopyridine nucleotide-dependent malic enzyme (DME, EC 1.1.1.39) and the triphosphopyridine nucleotide-dependent malic enzyme (TME, EC 1.1.1. 40) of Rhizobium (Sinorhizobium) meliloti. The predicted DME and TME proteins contain 770 and 764 amino acids, respectively, and are approximately 320 amino acids larger than previously characterized prokaryotic malic enzymes. The increased size of DME and TME resides in the C-terminal extensions which are similar in sequence to phosphotransacetylase enzymes (EC 2.3.1.8). Modified DME and TME proteins which lack this C-terminal region retain malic enzyme activity but are unable to oligomerize into the native state. Data base searches have revealed that similar chimeric malic enzymes were uniquely present in Gram-negative bacteria. Thus DME and TME appear to be members of a new class of malic enzyme characterized by the presence of a phosphotransacetylase-like domain at the C terminus of the protein.
苹果酸酶催化苹果酸氧化脱羧生成丙酮酸，并伴有烟酰胺辅因子的还原。我们测定了编码苜蓿中华根瘤菌二磷酸吡啶核苷酸依赖性苹果酸酶（DME，EC 1.1.1.39）和三磷酸吡啶核苷酸依赖性苹果酸酶（TME，EC 1.1.1.40）的基因的DNA序列和转录起始位点。预测的DME和TME蛋白分别含有770和764个氨基酸，比先前鉴定的原核苹果酸酶大约多320个氨基酸。DME和TME增加的大小存在于C末端延伸区，其序列与磷酸转乙酰酶（EC 2.3.1.8）相似。缺少该C末端区域的修饰DME和TME蛋白保留苹果酸酶活性，但不能寡聚成天然状态。数据库搜索表明，类似的嵌合苹果酸酶仅存在于革兰氏阴性细菌中。因此，DME和TME似乎是一类新的苹果酸酶成员，其特征是在蛋白质的C末端存在一个磷酸转乙酰酶样结构域。
