Morehouse K M, Mason R P
Laboratory of Molecular Biophysics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Arch Biochem Biophys. 1990 Dec;283(2):306-10. doi: 10.1016/0003-9861(90)90647-h.
The anaerobic enzymatic one-electron reduction of uroporphyrin I (in the absence of light) by the ferredoxin/ferredoxin:NADP+ oxidoreductase system was investigated using NADPH as the source of reducing equivalents. The porphyrin anion free radical metabolite formed by one-electron reduction of the parent molecule was detected with ESR spectroscopy. The ESR spectrum exhibited a singlet (g = 2.0021) with a 5.4-G peak-to-peak linewidth. The reduction process was also investigated under aerobic conditions. The reduction of molecular oxygen to superoxide anion radical by the porphyrin anion radical was demonstrated by using the ESR technique of spin trapping. The ESR spectra of the spin-trapped oxygen-derived radicals were superoxide dismutase-sensitive and catalase-insensitive, supporting the assignment of the trapped radical to the superoxide anion radical. These aerobic experiments demonstrate electron transfer from the porphyrin anion radical to molecular oxygen. The anaerobic reduction of Photofrin II by hepatic microsomes and the ferredoxin/ferredoxin:NADP+ oxidoreductase system to a porphyrin anion radical was also investigated. Free radical formation by ferredoxin: NADP+ oxidoreductase is totally dependent upon ferredoxin. The ESR spectrum of this porphyrin free radical also exhibited a singlet (g = 2.0026) with a 15-G peak-to-peak linewidth.
以NADPH作为还原当量的来源，研究了铁氧化还原蛋白/铁氧化还原蛋白：NADP⁺氧化还原酶系统在无氧条件下对尿卟啉I的酶促单电子还原反应（无光条件下）。通过电子顺磁共振光谱法检测了母体分子经单电子还原形成的卟啉阴离子自由基代谢产物。电子顺磁共振光谱显示为单重态（g = 2.0021），峰 - 峰线宽为5.4 G。还在有氧条件下研究了还原过程。通过自旋捕获电子顺磁共振技术证实了卟啉阴离子自由基将分子氧还原为超氧阴离子自由基。自旋捕获的氧衍生自由基的电子顺磁共振光谱对超氧化物歧化酶敏感，对过氧化氢酶不敏感，这支持了捕获的自由基为超氧阴离子自由基的认定。这些有氧实验证明了电子从卟啉阴离子自由基转移到分子氧。还研究了肝微粒体和铁氧化还原蛋白/铁氧化还原蛋白：NADP⁺氧化还原酶系统对二血卟啉醚的无氧还原反应，生成卟啉阴离子自由基。铁氧化还原蛋白：NADP⁺氧化还原酶形成自由基完全依赖于铁氧化还原蛋白。该卟啉自由基的电子顺磁共振光谱也显示为单重态（g = 2.0026），峰 - 峰线宽为15 G。
