ABSTRACT

The fundamental physical factors that govern reactions are most easily comprehended through use of energy-level diagrams. The free energy change of a reaction provides the drive toward equilibrium. Measurements of the binding of various ligands to Mb had been made for several decades before the fluctuating-structure, multistep binding process was discovered. The process of ligand binding to Mb, the “hydrogen atom of enzymes,” is clearly complex and should be treated with some detail. Such treatment is experimentally and analytically demanding, compared to what is needed for the application of single-step reaction theory. As a result, many scientists reverted to the idea of a rate-determining step in the binding process, especially when faced with hundreds of samples that needed to be measured and analyzed. Quantum-mechanical tunneling occurs when a particle crosses an energy barrier by virtually passing through the barrier, rather than over the barrier, as in the activated, thermodynamic processes.