title: Tryptophan-to-heme electron transfer in ferrous myoglobins.
abstract: It was recently demonstrated that in ferric myoglobins (Mb) the fluorescence quenching of the photoexcited tryptophan 14 (*Trp(14)) 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 π [Fe(II)(porph(●-))] -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 (Leu(69)) and valine 68 (Val(68)) residues. The results on ferric Mbs and the present ones highlight the generality of Trp-porphyrin electron transfer in heme proteins.
authors.affiliation: Laboratoire de Spectroscopie Ultrarapide, Institut de Sciences et Ingéniérie Chimiques, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Roberto
authors.initials: R
authors.lastname: Monni
authors.affiliation: Laboratoire de Spectroscopie Ultrarapide, Institut de Sciences et Ingéniérie Chimiques, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: André
authors.initials: A
authors.lastname: Al Haddad
authors.affiliation: Laboratoire de Spectroscopie Ultrarapide, Institut de Sciences et Ingéniérie Chimiques, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Frank
authors.initials: F
authors.lastname: van Mourik
authors.affiliation: Laboratoire de Spectroscopie Ultrarapide, Institut de Sciences et Ingéniérie Chimiques, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Gerald
authors.initials: G
authors.lastname: Auböck
authors.affiliation: Laboratoire de Spectroscopie Ultrarapide, Institut de Sciences et Ingéniérie Chimiques, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland majed.chergui@epfl.ch.
authors.forename: Majed
authors.initials: M
authors.lastname: Chergui
mesh_terms: D000465:Algorithms; D004579:Electron Transport; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D007700:Kinetics; D007930:Leucine / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry; D014364:Tryptophan / Q000737:chemistry*; D014633:Valine / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D009211:Myoglobin; D011166:Porphyrins; C055547:deoxymyoglobin; D006418:Heme; D014364:Tryptophan; D007930:Leucine; D014633:Valine
keywords: electron transfer; heme proteins; low valence heme; picosecond; tryptophan