Abstract Myoglobin, Mössbauer Spectroscopy, Recombination Kinetic Myoglobin-CO (MbCO) has been photodissoziated with white and monochromatic light at low temperatures (5-40 °K). The photoproduct Mb* was identified with Mössbauer spectroscopy as ferrous high-spin complex, with isomer shift and quadrupole splitting, which are similar to the corresponding parameters of deoxymyoglobin. From the time-dependent change of the linewidth of the Mb*-Mössbauer-spectrum at 5 °K over a time-intervall of 7 hours we conclude, that there exist several slightly different Mb*-conformations with different recombination characteristics. In order to obtain a convenient time resolution of the recombination behavior, we investigate the time-dependence of one of the Mb*-absorptionlines with a Mössbauer drive of constant velocity. The resulting recombination data then are analzyed in various steps of approximation. It is shown that at least two independent exponentials are necessary for the interpretation of experimental data. The attempt to interprete the experimental data on the basis of distribution of energies is in qualitative agreement with corresponding results, which are derived from optical recombination data by Austin et al. Typical activation energies for the recombination process CO → Mb* are 2 kcal/mol. At low temperature (T < 46 °K) the recombination behavior is explained by quantum-mechanical tunneling.
