NONEXPONENTIAL NON-ARRHENIUS RELAXATION IN THE COURSE OF CO REBINDINGTO HEME-PROTEINS

The dispersive transport model for relaxation of photolyzed heme prote ins has been improved to take into account the coupling of the ligand- heme geminate recombination and the non-Gaussian diffusive dynamics of conformational changes in heme proteins. Contrary to the earlier dete rministic version of the model, the present more rigorous formulation is based on the stochastic approach to the problem. This implies that the time evolution of protein conformations should be described in ter ms of the transient distribution which satisfies the Smoluchowski-type differential equation with a time-dependent diffusion coefficient. Th e obtained analytical solution of this equation enables us to relate m ain kinetic parameters of the geminate recombination and quantities ch aracterizing the ligand-heme interaction. The derived expressions demo nstrate that the reaction barrier shifts with time towards higher valu es following the near-stretched exponential behavior in agreement with experiment. Such a behavior is governed by the non-exponential non-Ar rhenius conformational relaxation, The latter process can be identifie d by the characteristic ''footprint'' left on the experimental rebindi ng curve and is shown to be responsible for some kinetically different phases of the ligand-heme geminate recombination observed within dist inct temperature ranges.