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Rapid Decay of the Native Intermediate in the Metallooxidase Fet3p Enables Controlled FeII Oxidation for Efficient Metabolism
journal contribution
posted on 2020-05-22, 22:04 authored by Stephen
M. Jones, David E. Heppner, Kenny Vu, Daniel J. Kosman, Edward I. SolomonThe multicopper oxidases (MCOs) couple
four 1e– oxidations of substrate
to the 4e– reduction of O2 to H2O.
These divide into two groups: those that oxidize organic substrates
with high turnover frequencies (TOFs) up to 560 s–1 and those that oxidize metal ions with low TOFs, ∼1 s–1 or less. The catalytic mechanism of the organic oxidases
has been elucidated, and the high TOF is achieved through rapid intramolecular
electron transfer (IET) to the native intermediate (NI), which only
slowly decays to the resting form. Here, we uncover the factors that
govern the low TOF in Fet3p, a prototypical metallooxidase, in the
context of the MCO mechanism. We determine that the NI decays rapidly
under optimal turnover conditions, and the mechanism thereby becomes
rate-limited by slow IET to the resting enzyme. Development of a catalytic
model leads to the important conclusions that proton delivery to the
NI controls the mechanism and enables the slow turnover in Fet3p that
is functionally significant in Fe metabolism enabling efficient ferroxidase
activity while avoiding ROS generation.