Reichard P
Department of Biochemistry I, Karolinska Institute, Stockholm, Sweden.
Science. 1993 Jun 18;260(5115):1773-7. doi: 10.1126/science.8511586.
It is generally accepted that DNA appeared after RNA during the chemical evolution of life. To synthesize DNA, deoxyribonucleotides are required as building blocks. At present, these are formed from the corresponding ribonucleotides through the enzymatic action of ribonucleotide reductases. Three classes of enzymes are present in various organisms. There is little sequence similarity among the three classes of reductases. However, enzymic mechanisms and the allosteric behavior of the enzymes from various organisms are strongly conserved, suggesting that the enzymes might have evolved from a common ancestor, with the class III anaerobic Escherichia coli reductase as its closest relative.
人们普遍认为，在生命的化学进化过程中，DNA是在RNA之后出现的。要合成DNA，需要脱氧核糖核苷酸作为构建模块。目前，这些是通过核糖核苷酸还原酶的酶促作用由相应的核糖核苷酸形成的。三类酶存在于各种生物体中。这三类还原酶之间几乎没有序列相似性。然而，各种生物体中酶的酶促机制和别构行为却高度保守，这表明这些酶可能起源于一个共同的祖先，其中III类厌氧大肠杆菌还原酶是其最接近的亲属。
