Narasimhan J, Antholine W E, Chitambar C R, Petering D H
National Biomedical Electron Spin Resonance Center, Medical College of Wisconsin, Milwaukee 53226.
Arch Biochem Biophys. 1991 Sep;289(2):393-8. doi: 10.1016/0003-9861(91)90429-m.
The electron paramagnetic resonance (EPR) signal of the tyrosyl radical attributed to ribonucleoside diphosphate reductase decreases after treatment of promyelocytic leukemic HL60 cells with 2-formylpyridine thiosemicarbazonato copper(II) (CuL). According to EPR studies, CuL forms adducts with both histidine and cysteine-like Lewis bases associated with isolated membranes from HL60 cells. After the addition of CuL, the EPR signal for the cysteine-like adduct decreases substantially over a 15-min period. The reduction of signal is consistent with oxidation of thiols as shown by an analysis of sulfhydryl content. It is hypothesized that receptor-mediated transferrin internalization is inhibited by oxidation of critical thiols. Since the uptake of 59Fe-transferrin is greatly inhibited by the treatment of HL60 cells with CuL, the reduced uptake of iron by cells, in the presence of CuL, may lead to decreased iron availability for the activity of the M2 subunit of ribonucleotide reductase and a subsequent decrease in the tyrosyl radical signal of the enzyme. Moreover, the intact subunit M2 is no longer detected by EPR, even after the addition of excess iron.
用2-甲酰基吡啶硫代半卡巴腙铜（II）（CuL）处理早幼粒细胞白血病HL60细胞后，归因于核糖核苷二磷酸还原酶的酪氨酸自由基的电子顺磁共振（EPR）信号减弱。根据EPR研究，CuL与来自HL60细胞的分离膜相关的组氨酸和半胱氨酸样路易斯碱形成加合物。添加CuL后，半胱氨酸样加合物的EPR信号在15分钟内大幅下降。信号的降低与硫醇的氧化一致，这通过巯基含量分析得以证明。据推测，关键硫醇的氧化会抑制受体介导的转铁蛋白内化。由于用CuL处理HL60细胞会极大地抑制59Fe-转铁蛋白的摄取，因此在存在CuL的情况下，细胞对铁的摄取减少可能会导致核糖核苷酸还原酶M2亚基活性的铁可用性降低，进而导致该酶的酪氨酸自由基信号下降。此外，即使添加过量铁后，EPR也不再检测到完整的M2亚基。
