Proton transfer at helium temperatures during dioxygen activation by heme monooxygenases.
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 approximately 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 (lambda in Marcus-like equations) and protein fluctuations ("active dynamics"; gating) which modulate the distance of proton transfer.
Davydov
Roman
R
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
Chemerisov
Sergey
S
Werst
David E
DE
Rajh
Tijana
T
Matsui
Toshitaka
T
Ikeda-Saito
Masao
M
Hoffman
Brian M
BM
D019475:Camphor 5-Monooxygenase / Q000737:chemistry / Q000378:metabolism; D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry / Q000378:metabolism*; D009211:Myoglobin / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D010108:Oxyhemoglobins / Q000737:chemistry / Q000378:metabolism
D009211:Myoglobin; D010108:Oxyhemoglobins; C017595:oxymyoglobin; D006419:Heme Oxygenase (Decyclizing); D019475:Camphor 5-Monooxygenase; D010100:Oxygen