Time-resolved visible and infrared study of the cyano complexes of myoglobin and of hemoglobin I from Lucina pectinata |
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Authors: | Helbing Jan Bonacina Luigi Pietri Ruth Bredenbeck Jens Hamm Peter van Mourik Frank Chaussard Frédéric Gonzalez-Gonzalez Alejandro Chergui Majed Ramos-Alvarez Cacimar Ruiz Carlos López-Garriga Juan |
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Affiliation: | Physikalisch-Chemisches Institut, Universit?t Zürich, 8057 Zürich, Switzerland. j.helbing@pci.unizh.ch |
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Abstract: | 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 triple bond 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 triple bond 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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