Proton transfer at helium temperatures during dioxygen activation by heme monooxygenases

Roman Davydov, Sergey Chemerisov, David E. Werst, Tijana Rajh, Toshitaka Matsui, Masao Ikeda-Saito, Brian M. Hoffman

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


In the first measurement of enzymatic proton transfer at liquid helium temperatures, we examine protonation of the peroxo-ferriheme state of heme oxygenase (HO) produced by in situ radiolytic cryoreduction of oxy-HO in H2O and D2O solvents at ca. 4 K and above, and compare these findings with analogous measurements for oxy-P450cam and for oxy-Mb. Proton transfer in HO occurs at helium temperatures in both solvents; it occurs in P450cam at ∼50 K and higher; in Mb it does not occur until T > 170 K. For Mb, this transfer at 180 K is biphasic, and the majority phase shows a solvent kinetic isotope effect of 3.8. We discuss these results in the context of the picture of environmentally coupled tunneling, which links proton transfer to two classes of protein motions: environmental reorganization (λ in Marcus-like equations) and protein fluctuations ("active dynamics"; gating) which modulate the distance of proton transfer.

Original languageEnglish (US)
Pages (from-to)15960-15961
Number of pages2
JournalJournal of the American Chemical Society
Issue number49
StatePublished - Dec 15 2004
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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