Seminars Archive

Transient absorption and broadband UV 2D spectroscopy of aqueous Mb

Abstract
Myoglobin (Mb) is a small protein consisting of a single polypeptide chain and an iron porphyrin (haem), which is its active site. The Fe can bind a large variety of small molecules (O2, as during its physiological role, CO, NO, CN…) and among them water (met Mb). The biological relevance and simplicity compared to other proteins made it the ‘H atom of biology’ [1]. Despite being one of the most studied proteins, the early haem relaxation pathways following photo-excitation are still subject to controversies [2, 3]. We performed UV/vis transient absorption experiments on ferric aqueous Mb (met Mb), and measurements on a newly developed UV 2D transient absorption setup, which is unique in the world. The successful combination of detection over a very broad spectral range (several tens of nm) with a target analysis revealed a branching in the ultrafast haem relaxation and allowed us to propose a new photocycle for its decay. Mb contains two Trp residues, which are believed to undergo energy transfer to the haem [4]. The possibility to excite and detect in the spectral region of Trp absorption opens new possibilities in the investigation of the cross-talks between these aminoacids and the haem prosthetic group. To this purpose, we developed a UV 2D setup which, depending on the sample, can cover in a single measurement a range of 70-80 nm and 80-100 nm along the pump and probe axis, respectively. The setup will be briefly presented, and some preliminary results will be shown. Bibliography [1] H. Frauenfelder, B. H. McMahon and P. W. Fenimore, Proceedings of the National Academy of Sciences of the United States of America 100 (2003), p. 8615. [2] Y. Kholodenko, M. Volk, E. Gooding and R. M. Hochstrasser, Chemical Physics 259 (2000), p. 71. [3] S. Ishizaka, T. Wada and N. Kitamura, Photochemical & Photobiological Sciences 8 (2009), p. 562. [4] R. M. Hochstrasser and D. K. Negus. Proceedings of the National Academy of Sciences of the United States of America 81 (1984), p. 4399.