PDF(Pubmed)
Abstract：
All forms of life are presumed to synthesize arginine from citrulline via a two-step pathway consisting of argininosuccinate synthetase and argininosuccinate lyase using citrulline, adenosine 5\'-triphosphate (ATP), and aspartate as substrates. Conversion of arginine to citrulline predominantly proceeds via hydrolysis. Here, from the hyperthermophilic archaeon Thermococcus kodakarensis, we identified an enzyme which we designate \"arginine synthetase\". In arginine synthesis, the enzyme converts citrulline, ATP, and free ammonia to arginine, adenosine 5\'-diphosphate (ADP), and phosphate. In the reverse direction, arginine synthetase conserves the energy of arginine deimination and generates ATP from ADP and phosphate while releasing ammonia. The equilibrium constant of this reaction at pH 7.0 is [Cit][ATP][NH3]/[Arg][ADP][Pi] = 10.1 ± 0.7 at 80 °C, corresponding to a ΔG°\' of -6.8 ± 0.2 kJ mol-1. Growth of the gene disruption strain was compared to the host strain in medium composed of amino acids. The results suggested that arginine synthetase is necessary in providing ornithine, the precursor for proline biosynthesis, as well as in generating ATP. Growth in medium supplemented with citrulline indicated that arginine synthetase can function in the direction of arginine synthesis. The enzyme is widespread in nature, including bacteria and eukaryotes, and catalyzes a long-overlooked energy-conserving reaction in microbial amino acid metabolism. Along with ornithine transcarbamoylase and carbamate kinase, the pathway identified here is designated the arginine synthetase pathway.
摘要：
推测所有形式的生命都是通过由精氨酸琥珀酸合成酶和精氨酸琥珀酸裂解酶组成的两步途径从瓜氨酸合成精氨酸，5'-三磷酸腺苷（ATP），和天冬氨酸作为底物。精氨酸向瓜氨酸的转化主要通过水解进行。这里,来自高热嗜热古细菌，我们确定了一种酶，我们称之为“精氨酸合成酶”。在精氨酸合成中,酶转化瓜氨酸，ATP,游离氨和精氨酸，5'-二磷酸腺苷（ADP），和磷酸盐。在相反的方向，精氨酸合成酶保存精氨酸脱亚胺的能量，并从ADP和磷酸盐产生ATP，同时释放氨。该反应在pH7.0时的平衡常数为[Cit][ATP][NH3]/[Arg][ADP][Pi]=10.1±0.7,对应于-6.8±0.2kJmol-1的ΔG°\'。在由氨基酸组成的培养基中将基因破坏菌株的生长与宿主菌株进行比较。结果表明，精氨酸合成酶是提供鸟氨酸所必需的，脯氨酸生物合成的前体，以及产生ATP。在补充瓜氨酸的培养基中的生长表明精氨酸合成酶可以在精氨酸合成的方向上发挥作用。这种酶在自然界中普遍存在，包括细菌和真核生物,并催化微生物氨基酸代谢中长期被忽视的节能反应。随着鸟氨酸转氨酰基转移酶和氨基甲酸酯激酶，此处鉴定的途径称为精氨酸合成酶途径。
