The dynamics of carbon monoxide binding to hemoglobin and to cytochrome

Ephraim Buhks, Joshua Jortner

Research output: Contribution to journalArticlepeer-review


In this paper we apply the theory of nonadiabatic multiphonon group transfer processes to describe the low temperature recombination reaction between CO and hemoglobin (CO-Hb) and between CO and carboxylmethyl cytochrome c (CO-cmcytc). The CO-Hb recombination is accompanied by an electronic transition from an S=2 high spin "free" state to an S=0 low open "bound" state, with the iron heme moving from a domed-type structure into a planar structure, while the characteristic low frequency of relevant vibration mode(s) involving the heme iron coupled to the protein (〈ω〉≅50 cm-1). The CO-cmcytc recombination characterized by an electronic transition from an S=1 spin free state to an S=0 bound state, with the iron heme ring staying planar and configurational frequencies prevail for a high-frequency (ωc≅400 cm-1) in-plane iron-porphyrin vibrational mode. The distinct electronic and nuclear parameters for these two recombination processes account for the large difference in the onset of the temperature dependent rate for the CO-Hb (10 K) and for the CO-cmcytc (40 K) systems, as well as for the five orders of magnitude increase in the low-temperature, temperature independent tunneling rate constant for CO-cmcytc relative to the CO-Hb recombination process.

Original languageEnglish
Pages (from-to)4456-4462
Number of pages7
JournalThe Journal of Chemical Physics
Issue number9
StatePublished - 1985


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