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Biophysical Journal 87:1881-1891 (2004)
© 2004 The Biophysical Society

Time-Resolved Visible and Infrared Study of the Cyano Complexes of Myoglobin and of Hemoglobin I from Lucina pectinata

Jan Helbing *, Luigi Bonacina {dagger}, Ruth Pietri {ddagger}, Jens Bredenbeck *, Peter Hamm *, Frank van Mourik {dagger}, Frédéric Chaussard {dagger}, Alejandro Gonzalez-Gonzalez {dagger}, Majed Chergui {dagger}, Cacimar Ramos-Alvarez {ddagger}, Carlos Ruiz {ddagger} and Juan López-Garriga {ddagger}

* Physikalisch-Chemisches Institut, Universität Zürich, Zürich, Switzerland; {dagger} Laboratoire de Spectroscopie Ultrarapide, Institut des Sciences et Ingénierie Chimiques, Faculté des Sciences de Base, Ecole Polytechnique Fédérale de Lausanne, Lausanne-Dorigny, Switzerland; and {ddagger} Chemistry Department, University of Puerto Rico, Mayagüez, Puerto Rico

Correspondence: Address reprint requests to Jan Helbing, Dept. of Physical Chemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. Tel.: 41-1-635-4471; E-mail: j.helbing{at}pci.unizh.ch.

The dynamics of the ferric CN complexes of the heme proteins Myoglobin and Hemoglobin I from the clam Lucina pectinata upon Soret band excitation is monitored using infrared and broad band visible pump-probe spectroscopy. The transient response in the UV-vis spectral region does not depend on the heme pocket environment and is very similar to that known for ferrous proteins. The main feature is an instantaneous, broad, short-lived absorption signal that develops into a narrower red-shifted Soret band. Significant transient absorption is also observed in the 360–390 nm range. At all probe wavelengths the signal decays to zero with a longest time constant of 3.6 ps. The infrared data on MbCN reveal a bleaching of the C {equiv} N stretch vibration of the heme-bound ligand, and the formation of a five-times weaker transient absorption band, 28 cm–1 lower in energy, within the time resolution of the experiment. The MbC {equiv} N stretch vibration provides a direct measure for the return of population to the ligated electronic (and vibrational) ground state with a 3–4 ps time constant. In addition, the CN-stretch frequency is sensitive to the excitation of low frequency heme modes, and yields independent information about vibrational cooling, which occurs on the same timescale.




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