ABSTRACT
The transfer of atoms or molecules is important in biological processes. Ligand substitution, that is, the transfer of heavy molecular groups is important in the binding of substrate molecules by metal centers of hydrolytic metalloenzymes. Transport of the atoms to the reaction zone is usually adiabatic proceeding on the lower energy surface playing the role of potential relief for the moving atom. In the motion of atoms in macromolecules steric restrictions may arise due to smaller equilibrium values of the interatomic distances in the macromolecule than the size of the diffusing particle. The reversible binding of carbon monoxide and oxygen by hemoglobin and myoglobin is one of the examples of atom group transfer in macromolecules. The reaction proceeds under conditions where the theory of electron-vibrational transitions is applicable. Both the vibrational modes of the reaction complex and a continuous set of soft vibrational modes of the medium take part in the reaction.
