Evidence for protein radical-mediated nuclear tunneling in fatty acid alpha-oxygenase |
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Authors: | Gupta Ankur Mukherjee Arnab Matsui Kenji Roth Justine P |
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Affiliation: | Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore Maryland 21218, USA. |
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Abstract: | Rice alpha-oxygenase (RalphaO) catalyzes the insertion of O2 into the Calpha-H bond of various fatty acids. The mechanism is thought to involve a tyrosyl radical as the oxidant on the basis of comparisons to the structurally homologous cyclooxygenase enzymes. Kinetic and spectroscopic results presented here for the wild-type RalphaO and the Tyr379Phe mutant indicate an irreversible H* abstraction mechanism and support the involvement of the proposed catalytic Tyr*. In addition, very large, weakly temperature dependent deuterium kinetic isotope effects (approximately 50) are observed, consistent with extensive nuclear tunneling. RalphaO, thus, presents a novel example where such quantum effects are associated with an amino acid radical-utilizing enzyme. |
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