期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：18
页码：5602-5606
DOI：10.1073/pnas.1423186112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceWe demonstrate the occurrence of tryptophan (Trp) to heme electron transfer (ET) in ferrous myoglobins by ultrafast UV spectroscopy. The ET gives rise to the theoretically predicted, low-valence Fe(II)(porph[bullet]-) anion radical, which we observe for the first time to our knowledge under physiological conditions. These results highlight the generality of Trp-porphyrin electron transfer events in heme proteins and question the systematic use of Trp fluorescence in FRET studies of protein dynamics. It was recently demonstrated that in ferric myoglobins (Mb) the fluorescence quenching of the photoexcited tryptophan 14 (*Trp14) residue is in part due to an electron transfer to the heme porphyrin (porph), turning it to the ferrous state. However, the invariance of *Trp decay times in ferric and ferrous Mbs raises the question as to whether electron transfer may also be operative in the latter. Using UV pump/visible probe transient absorption, we show that this is indeed the case for deoxy-Mb. We observe that the reduction generates (with a yield of about 30%) a low-valence Fe-porphyrin {pi} [FeII(porph[bullet]-)] -anion radical, which we observe for the first time to our knowledge under physiological conditions. We suggest that the pathway for the electron transfer proceeds via the leucine 69 (Leu69) and valine 68 (Val68) residues. The results on ferric Mbs and the present ones highlight the generality of Trp-porphyrin electron transfer in heme proteins.
