Ultrafast CO Kinetics in Heme Proteins: Adiabatic Ligand Binding and Heavy Atom Tunneling.

ABSTRACT: The ultrafast kinetics of CO rebinding to carbon monoxide oxidation activator protein (ChCooA) are measured over a wide temperature range and compared with the kinetics of CO binding in other heme systems such as myoglobin (Mb) and hemoglobin (Hb). The Arrhenius prefactor for CO binding to ChCooA and protoheme (∼10¹¹ s^-1) is similar to what is found for spin-allowed NO binding to heme proteins and is several orders of magnitude larger than the prefactor of Mb and Hb (∼10⁹ s^-1). This indicates that the CO binding reaction is adiabatic, in contrast to the commonly held view that it is nonadiabatic due to spin-forbidden (ΔS = 2) selection rules. Under the adiabatic condition, entropic factors, rather than spin-selection rules, are the source of the

SUBMITTER: Benabbas A 

PROVIDER: S-EPMC5976446 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature