Time-resolved visible and infrared study of the cyano complexes of myoglobin and of hemoglobin I from Lucina pectinata.
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.
Helbing
Jan
J
Physikalisch-Chemisches Institut, Universität Zürich, 8057 Zürich, Switzerland. j.helbing@pci.unizh.ch
Bonacina
Luigi
L
Pietri
Ruth
R
Bredenbeck
Jens
J
Hamm
Peter
P
van Mourik
Frank
F
Chaussard
Frédéric
F
Gonzalez-Gonzalez
Alejandro
A
Chergui
Majed
M
Ramos-Alvarez
Cacimar
C
Ruiz
Carlos
C
López-Garriga
Juan
J
D000818:Animals; D004583:Electrons; D006418:Heme / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry*; D006736:Horses; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D007834:Lasers; D008974:Mollusca; D018482:Muscle, Skeletal / Q000378:metabolism; D009211:Myoglobin / Q000737:chemistry*; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors; D014466:Ultraviolet Rays
D006454:Hemoglobins; D009211:Myoglobin; D006418:Heme; D007501:Iron