Voevodskaya Nina, Lendzian Friedhelm, Ehrenberg Anders, Gräslund Astrid
Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
FEBS Lett. 2007 Jul 24;581(18):3351-5. doi: 10.1016/j.febslet.2007.06.023. Epub 2007 Jun 21.
Ribonucleotide reductase (class I) contains two components: protein R1 binds the substrate, and protein R2 normally has a diferric site and a tyrosyl free radical needed for catalysis. In Chlamydia trachomatis RNR, protein R2 functions without radical. Enzyme activity studies show that in addition to a diiron cluster, a mixed manganese-iron cluster provides the oxidation equivalent needed to initiate catalysis. An EPR signal was observed from an antiferromagnetically coupled high-spin Mn(III)-Fe(III) cluster in a catalytic reaction mixture with added inhibitor hydroxyurea. The manganese-iron cluster in protein R2 confers much higher specific activity than the diiron cluster does to the enzyme.
核糖核苷酸还原酶（I类）包含两个组分：蛋白质R1结合底物，蛋白质R2通常具有催化所需的双铁位点和酪氨酸自由基。在沙眼衣原体核糖核苷酸还原酶中，蛋白质R2在没有自由基的情况下发挥作用。酶活性研究表明，除了双铁簇外，混合的锰 - 铁簇提供启动催化所需的氧化当量。在添加抑制剂羟基脲的催化反应混合物中，从反铁磁耦合的高自旋Mn(III)-Fe(III)簇观察到一个电子顺磁共振信号。蛋白质R2中的锰 - 铁簇赋予该酶比双铁簇更高的比活性。
