Proton transfer at helium temperatures during dioxygen activation by heme monooxygenases.
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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.
author list (cited authors)
Davydov, R., Chemerisov, S., Werst, D. E., Rajh, T., Matsui, T., Ikeda-Saito, M., & Hoffman, B. M
complete list of authors
Davydov, Roman||Chemerisov, Sergey||Werst, David E||Rajh, Tijana||Matsui, Toshitaka||Ikeda-Saito, Masao||Hoffman, Brian M