Anderson G L, Howard J B
Biochemistry. 1984 May 8;23(10):2118-22. doi: 10.1021/bi00305a002.
The Fe-S center of oxidized Fe protein from Azotobacter vinelandii nitrogenase is decomposed by alpha,alpha'-dipyridyl in a biphasic process. In the presence of MgATP, 2 Fe are immediately removed by chelation while the additional irons are removed only after several hours. A slower biphasic Fe release also was observed in the presence of chelator alone. MgADP prevented the Fe release by chelator. An intermediate in the reaction was isolated containing 2 Fe. The visible spectrum of the intermediate was similar to that of 2Fe-2S ferredoxins (epsilon max at 325, 416, and 460 nm of 16.1, 11.3, and 9.0 mM-1 cm-1). The 2Fe form was electron paramagnetic resonance (EPR) silent until partially reduced with sodium dithionite. The EPR spectral properties were similar to 2Fe-2S ferredoxins; namely, the Fe center had resonances at g = 2.00, 1.94, and 1.92 which were detectable, essentially unbroadened at 70 K. The results suggest that in the oxidized (2+) state Fe protein can undergo a 4Fe to 2Fe conversion.
来自棕色固氮菌固氮酶的氧化态铁蛋白的铁硫中心在双相过程中被α,α'-联吡啶分解。在MgATP存在下，2个铁会立即通过螯合作用被去除，而额外的铁只有在数小时后才会被去除。在仅存在螯合剂的情况下，也观察到了较慢的双相铁释放。MgADP可阻止螯合剂引起的铁释放。反应过程中分离出了一种含2个铁的中间体。该中间体的可见光谱与2Fe-2S铁氧化还原蛋白的相似（在325、416和460 nm处的εmax分别为16.1、11.3和9.0 mM-1 cm-1）。这种2Fe形式在被连二亚硫酸钠部分还原之前，电子顺磁共振（EPR）呈沉默状态。其EPR光谱特性与2Fe-2S铁氧化还原蛋白相似；即铁中心在g = 2.00、1.94和1.92处有共振峰，在70 K时可检测到，基本未展宽。结果表明，在氧化（2+）状态下，铁蛋白可经历从4Fe到2Fe的转变。
