Different relaxations in myoglobin after photolysis

To clarify the interplay of kinetic hole-burning (KHB), structural relaxation, and ligand migration in myoglobin (Mb), we measured time-resolved absorption spectra in the Soret region after photolysis of carbon monoxide Mb (MbCO) in the temperature interval 120-260 K and in the time window 350 ns to 200 ms. The spectral contributions of both photolyzed (Mb * ) and liganded Mb (MbCO) have been analyzed by taking into account homogeneous bandwidth, coupling to vibrational modes, and static conformational heterogeneity. We succeeded in separating the “time-dependent” spectral changes, and this work provides possibilities to identify the events in the process of ligand rebinding. KHB is domina…

Structural factors controlling ligand binding to myoglobin: a kinetic hole-burning study.

Using temperature-derivative spectroscopy in the temperature range below 100 K, we have studied the dependence of the Soret band on the recombination barrier in sperm whale carbonmonoxy myoglobin (MbCO) after photodissociation at 12 K. The spectra were separated into contributions from the photodissociated species, Mb*CO, and CO-bound myoglobin. The line shapes of the Soret bands of both photolyzed and liganded myoglobin were analyzed with a model that takes into account the homogeneous bandwidth, coupling of the electronic transition to vibrational modes, and static conformational heterogeneity. The analysis yields correlations between the activation enthalpy for rebinding and the model p…

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