The tyrosyl free radical in ribonucleotide reductase.
The tyrosyl free radical in ribonucleotide reductase.
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DOI：
10.1289/ehp.64-1568609
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发表时间：
1985-12
影响因子：
10.4
通讯作者：
Sjöberg BM
中科院分区：
文献类型：
--
作者：
Gräslund A;Sahlin M;Sjöberg BM
这种酶，核糖核苷酸还原酶，催化核糖核苷酸形成脱氧核糖核苷酸，这是所有活细胞中DNA合成所必需的反应。大肠杆菌核糖核苷酸还原酶是所有已知真核生物和病毒编码酶的原型，由两个不相同的亚基，蛋白质B1和B2组成。B2亚基含有一对反铁磁偶联的铁离子和一个稳定的酪氨酸自由基。EPR研究表明，酪氨酸自由基是由失去铁离子和稳定的酪氨酸自由基形成的。EPR研究表明，由于失去一个电子而形成的酪氨酸自由基，其不成对的自旋密度在酪氨酸的芳环中离域。铁自由基相互作用的影响表明铁中心与自由基之间的距离相对较近。如果使细胞过量产生核糖核苷酸还原酶，则可以在大肠杆菌或哺乳动物源的冷冻包装细胞中直接研究自由基的EPR信号。除了与抑制底物类似物2'-叠氮- cdp的反应外，酪氨酸自由基在酶促反应中的假设作用尚未阐明。在这种情况下，正常的酪氨酸自由基被破坏，同时出现2'-叠氮- cdp定位的自由基中间体。对自由基反应中间体的自旋捕获的尝试结果是否定的。在大肠杆菌中，核糖核苷酸还原酶的活性可能受到非自由基形式与完全活性蛋白B2相互转化的酶活性的调节。然而，在同步的哺乳动物细胞中，EPR研究的核糖核苷酸还原酶的细胞周期变化被证明是由于从头合成蛋白质。核糖核苷酸还原酶抑制剂因其控制DNA合成的能力而引起医学上的兴趣。一个例子是用于癌症治疗的羟基脲，它选择性地破坏酪氨酸自由基。
The enzyme, ribonucleotide reductase, catalyses the formation of deoxyribonucleotides from ribonucleotides, a reaction essential for DNA synthesis in all living cells. The Escherichia coli ribonucleotide reductase, which is the prototype of all known eukaryotic and virus-coded enzymes, consists of two nonidentical subunits, proteins B1 and B2. The B2 subunit contains an antiferromagnetically coupled pair of ferric ions and a stable tyrosyl free radical. EPR studies show that the tyrosyl radical, formed by loss of ferric ions and a stable tyrosyl free radical. EPR studies show that the tyrosyl radical, formed by loss of an electron, has its unpaired spin density delocalized in the aromatic ring of tyrosine. Effects of iron-radical interaction indicate a relatively close proximity between the iron center and the radical. The EPR signal of the radical can be studied directly in frozen packed cells of E. coli or mammalian origin, if the cells are made to overproduce ribonucleotide reductase. The hypothetic role of the tyrosyl free radical in the enzymatic reaction is not yet elucidated, except in the reaction with the inhibiting substrate analogue 2'-azido-CDP. In this case, the normal tyrosyl radical is destroyed with concomitant appearance of a 2'-azido-CDP-localized radical intermediate. Attempts at spin trapping of radical reaction intermediates have turned out negative. In E. coli the activity of ribonucleotide reductase may be regulated by enzymatic activities that interconvert a nonradical containing form and the fully active protein B2. In synchronized mammalian cells, however, the cell cycle variation of ribonucleotide reductase, studied by EPR, was shown to be due to de novo protein synthesis. Inhibitors of ribonucleotide reductase are of medical interest because of their ability to control DNA synthesis. One example is hydroxyurea, used in cancer therapy, which selectively destroys the tyrosyl free radical.